LIBRARY 

,  OF  THE 

UNIVERSITY  OF  CALIFORNIA. 


Class 


NOTES 


ON 


ELECTROCHEMISTKY 


BY 


F.  G.  WIECHMANN,  PH.D. 

\ 


NEW   YORK 

McGRAW    PUBLISHING    COMPANY 

190$ 


W5 


f>»- 


COPTBIGHT   1906, 

BY 

F.   G.   WlECHMANN 
All  rights  reserved. 


TO 

CHARLES  H.  SENFF 

A    TOKEN    OF 
ESTEEM    AND    REGARD 


PREFACE. 


THE  principal  aim  kept  in  view  in  the  preparation  of  these 
notes  has  been  the  giving  of  a  clear  and  concise  presentation 
of  the  general  principles  which  underlie  electrochemical 
science. 

Endeavor  has  been  made  to  meet  the  needs  of  students 
entering  upon  the  study  of  electrochemistry  and  of  chemists 
interested  in  the  application  of  electrical  energy  to  chemical 
problems. 

The  literature  of  electrochemistry  counts  as  its  own  a 
number  of  standard  works  which  treat  in  detail  the  theories 
of  the  science,  the  methods  of  electrochemical  analysis,  and 
the  applications  of  electrochemistry.  Differing  from  these, 
the  present  notes  aim  merely  to  offer  a  general  survey  of  the 
subject,  to  serve  as  an  introduction  to  its  study  and  to  aid 
in  the  securing  of  a  proper  understanding  and  appreciation 
of  the  work  along  individual  lines. 

In  the  chapter  on  electro  technology,  special  endeavor  has 
been  made  to  secure  the  most  recent  and  reliable  data  and 
full  advantage  has  been  taken  of  the  information  given  in 
leading  technical  journals  and  in  the  excellent  monographs 
of  Foerster:  Elektrochemie  Wasseriger  Losungen,  and  of 
Wright:  Electric  Furnaces  and  their  Industrial  Applications. 

It  must  however  not  be  forgotten  that  exact  data  of 
technical  operations  are  often  very  difficult  to  procure,  and 
therefore  the  figures  given,  while  well  indicating  the  general 
conditions  obtaining,  cannot  in  all  cases  claim  to  be  actual 
working  formulae. 

Prefacing  each  chapter  there  will  be  found  a  bibliography 


vi  PREFACE. 

of  important  treatises  bearing  upon  the  subject-matter  dis- 
cussed in  the  chapter.  The  works  so  indicated  have  all  been 
consulted  in  the  preparation  of  these  pages,  and  the  writer 
would  here  take  opportunity  to  express  his  obligations  to 
their  authors. 

F.  G.  W. 


TABLE    OF   CONTENTS. 


PREFACE    v 

CHAPTER  I.     GENERAL  PRINCIPLES 1 

General  Principles  of  Science  —  Matter  and  Energy  — 
Forms  of  Energy  —  Measurement  of  Physical  Phenomena. 

CHAPTER  II.     ELECTRICAL  ENERGY     ..." 8 

Theories  of  Electricity  —  Radio-activity  —  Factors  of  Elec- 
trical Energy  —  Properties  of  Electricity  —  Ohm's  Law. 

CHAPTER  III.     ELECTROCHEMISTRY 22 

Evolution  of  Electrochemistry  —  Electrolysis  —  Electro- 
motive Force  —  Dissociation  Voltage. 

CHAPTER  IV.     ELECTROLYTIC  DISSOCIATION 41 

The  Ion  Theory  —  Conductivity  —  Migration  of  Ions. 

CHAPTER  V.     ELECTRO-ANALYSIS 66 

Electro-analysis  —  Reversible  Reactions  and  Cells  — 
Sources  of  Current  —  Current  Measurement  —  Current 
Regulation  —  Electrodes  — •  Currrent  Density  —  Records 
—  Resume". 

CHAPTER  VI.     ELECTROTECHNOLOGY      93 

Introduction  —  Direct  Action  Processes  :  Electrodeposition 
from  Solution  —  Electroplating  —  Chlorine  and  Alkali 
Hydrates — Indirect  Action  Processes  :  Electrodeposition 
from  Fused  Electrolytes  —  Electrothermic  Processes  : 
Electro-furnaces  —  Electro- furnace  Products  —  Electro- 
Organic  Processes  :  Direct  Action  Processes  —  Silent  Dis- 
charge —  Electro-Osmosis. 

NAME  INDEX 139 

SUBJECT  INDEX  141 


vii 


THE 


UNIVERSITY 

J 

X^MFOP*. 


NOTES   ON   ELECTROCHEMISTRY. 


CHAPTER  I. 
GENERAL  PRINCIPLES. 

Literature:  BERING,  C.:  "Ready  Reference  Tables,"  Vol.  I.  New 
York,  1904.  HOLMAN,  S.  W.:  "  Matter,  Energy,  Force,  and 
Work."  New  York,  1898.  NOTES,  A.  A.:  "General  Principles  of 
Physical  Science."  New  York,  1902.  WHBTHAM,  W.  C.  D.: 
"The  Recent  Development  of  Physical  Science."  Philadelphia, 
1904. 

General  Principles  of  Science.  —  Before  taking  up  for  con- 
sideration the  subject  to  which  these  notes  are  to  be  devoted, 
it  will  not  prove  amiss  to  refer  briefly  to  some  of  the  general 
principles  which  underlie  electrochemistry,  as  they  do  all 
branches  of  physical  science. 

Science  is  defined  as  systematized  knowledge.  Physical 
science,  in  its  broader  aspect,  may  be  said  to  deal  with  all 
phenomena  of  nature,  the  Greek  word,  physis,  signifying  all 
nature.  Physical  science,  then,  seeks  to  give  a  thorough 
presentation  of  all  natural  phenomena,  and  to  formulate 
principles  which  will  permit  of  the  prediction  of  such  phe- 
nomena. 

There  are  two  methods  which  may  be  legitimately  followed 
in  scientific  investigation,  —  experience,  and  speculation  based 
on  experience.  These  two  methods  are  mutually  supple- 
mentary and  interdependent,  for,  reduced  to  final  terms,  all 
human  science  is  knowledge  based  on  experience. 

The  first  step  to  be  taken  in  experimental  investigation  is 
the  collection  and  accumulation  of  facts.  When  a  sufficient 
number  of  data  have  been  secured,  the  more  the  better,  the 

1 


2  NOTES  ON  ELECTROCHEMISTRY. 

proper  grouping  and  correlation  of  these  data  are  required. 
This  is  achieved  by  the  process  of  inductive  reasoning. 

Induction  consists  in  the  drawing  of  conclusions  from 
observed  facts,  in  the  inference  of  general  principles  from 
the  consideration  of  individual  cases. 

But  it  is  not  always  possible  to  apply  the  inductive  method, 
owing  to  the  great  number  and  the  complexity  of  natural 
phenomena,  and,  therefore,  recourse  is  often  had  to  another 
method  of  reasoning,  —  deduction. 

Deduction  consists  in  the  advancing  of  some  general  sup- 
position provisionally  adopted  to  account  for  certain  phe- 
nomena, and  then  submitting  such  supposition  to  the  test  of 
experiment. 

All  suppositions  of  this  kind  are  termed  hypotheses.  An 
hypothesis  is,  therefore,  merely  a  tentative  conjecture  as  to 
the  nature  and  cause  of  phenomena.  All  logical  deductions 
drawn  from  an  hypothesis,  unless  supported  by  experimental 
demonstration,  are  called  theories. 

The  crucial  test  as  to  the  value  and  validity  of  all  hypoth- 
eses and  theories  is,  of  course,  their  concordance  with  re- 
sults obtained  by  experiment.  Discovery  of  any  fact  or 
facts  not  in  agreement  with  the  tenets  of  a  given  hypothesis 
or  theory,  at  once  forces  the  modification  or  even  abandon- 
ment of  the  theory. 

Deduction,  then,  consists  in  the  derivation  of  specific  con- 
clusions from  a  more  general  proposition;  it  is  obviously  the 
inverse  of  induction. 

When  a  general  theory,  evolved  by  either  the  inductive  or 
the  deductive  method,  has  been  submitted  to  and  verified  by 
experimental  proof,  it  is  termed  a  law. 

A  law  must  not  only  embrace  all  known  facts  and  phe- 
nomena to  which  it  refers,  but  must  also  be  able  to  account 
for  all  phenomena  of  like  character  which  may  ever  be  dis- 
covered. In  fact,  a  law  must,  to  a  certain  extent,  be  capable 
of  predicting  such  phenomena. 


GENERAL  PRINCIPLES.  3 

A  law  is  simply  a  concise  expression  of  the  results  of  ex- 
perience. As  Whetham  has  so  ably  expressed  it:  "  We  must 
look  upon  natural  laws  merely  as  convenient  shorthand 
statements  of  the  organized  information  that  is  at  present  at 
our  disposal." 

Matter  and  Energy.  —  Matter  and  energy  are  primary  con- 
cepts employed  to  simplify  and  to  systematize  our  impres- 
sions of  natural  phenomena. 

The  two  fundamental  laws  of  physical  science  are  concerned 
with  these  concepts.  These  laws  are  the  law  of  the  conser- 
vation of  matter,  due  to  Lavoisier,  1789,  and  the  law  of  the 
conservation  of  energy,  due  to  Robert  Mayer,  1842.  The 
first  of  these  laws  holds  that  matter,  the  second,  that  energy, 
can  be  neither  created  nor  destroyed. 

If  we  are  willing  to  accept  an  inseparable  blending  of  mat- 
ter and  energy,  giving  to  this  concept  the  designation,  sub- 
stance, then  both  of  the  laws  given  may  be  incorporated  as 
one,  the  law  of  substance:  Substance  can  be  neither  created 
nor  destroyed.  This  law  of  substance  is  —  as  far  as  human 
reason  can  conceive  —  a  law  of  universal  validity,  a  law  of 
the  cosmos. 

Viewed  as  a  component  of  substance,  matter  must  be 
regarded  as  its  inert  constituent;  it  may  be  defined  as  that 
which  has  extension,  which  occupies  space,  which  constitutes 
the  tangible  portion  of  the  universe. 

Energy,  the  other  component  of  substance,  may  be  con- 
sidered as  the  cause  of  all  changes,  of  all  physical  phenomena. 
As  Maxwell  has  expressed  it:  "  Energy  .  .  .  that  which  in 
all  natural  phenomena  is  continually  passing  from  one  por- 
tion of  matter  to  another.  Energy  cannot  exist  except  in 
connection  with  matter." 

The  term  "  energy  "  was  first  introduced  by  Young,  in  1832, 
as  a  designation  of  the  product  mv2  (vis  viva) ;  in  the  sense 
in  which  it  is  now  commonly  accepted,  it  has  been  used  since 
about  1860. 


4  NOTES  ON  ELECTROCHEMISTRY. 

The  principle  of  the  conservation  of  energy,  or,  the  first 
law  of  energetics  as  it  is  sometimes  called,  was  first  formu- 
lated by  Robert  Mayer  as  a  broad  generalization  from  ex- 
perimental evidence.  About  1842  Joule  furnished  much 
direct  and  valuable  experimental  testimony  of  its  truth,  and 
every  test  ever  made  of  this  most  important  law  has  affirmed 
its  correctness. 

Forms  of  Energy.  —  Energy  appears  in  various  forme,  for 
instance  as  mechanical,  as  thermal,  as  chemical,  and  as  electri- 
cal energy.  These  forms  are  mutually  convertible,  and  when- 
ever a  given  quantity  of  some  one  kind  of  energy  disappears, 
an  exactly  equivalent  amount  of  some  one  other  or  of  several 
other  kinds  of  energy  appear. 

There  is,  however,  one  limitation  that  must  be  noted  in 
this  connection.  Whereas  all  forms  of  energy  can  be  trans- 
formed into  thermal  energy,  the  complete  changing  of  ther- 
mal energy  into  mechanical,  or  into  other  forms  of  energy, 
cannot  be  effected.  This  principle  is  known  as  the  second 
law  of  energetics. 

All  forms  of  energy  may  be  regarded  as  the  product  of 
two  factors,  intensity  and  capacity.  The  former  determines 
whether  the  energy  in  a  given  system  must  be  active  or  at 
rest;  the  capacity-factor  determines  the  quantity  of  energy 
present  in  a  given  system.  In  all  energy  transformations  a 
part  of  the  original  energy  is  changed  into  heat,  and  thus, 
eventually,  all  energy  is  doomed  to  pass  into  this  form;  at 
least  at  present  no  process  working  to  reverse  this  outcome 
is  known. 

Furthermore,  in  all  transformations  of  heat-energy  a  part 
of  this  energy  passes  to  a  lower  temperature;  radiation,  con- 
duction, and  convection  aiding  to  bring  about  this  result. 
Temperature,  however,  is  the  intensity-factor  of  thermal 
energy,  and,  as  no  work  can  be  obtained  from  heat  unless 
there  are  differences  in  temperature,  ultimately,  it  seems, 
all  energy  must  pass  into  the  form  of  diffused  heat.  When 


GENERAL  PRINCIPLES.  5 

this  shall  have  occurred,  the  universe  will  have  attained  to 
one  and  the  same  temperature,  and  then  all  life  and  motion 
must  come  to  an  end.  This  doctrine,  known  as  the  theory 
of  the  dissipation  or  the  degradation  of  energy,  was  first 
suggested  by  Sir  William  Thomson  (Lord  Kelvin). 

Measurement  of  Physical  Phenomena.  —  Besides  matter 
and  energy  there  are  two  fundamental  concepts  which  enter 
into  the  contemplation  of  every  physical  phenomenon  where  a 
quantitative  study  of  the  same  is  attempted.  These  con- 
cepts are  time  and  space.  Time  may  be  considered  as  a 
recognition  of  sequence  in  human  consciousness.  The  sim- 
plest form  of  the  concept  of  space  is  length. 

Time,  space,  and  mass  are  of  primary  importance  in  nearly 
all  measurements  of  physical  phenomena.  To  effect  such 
measurements  it  is  necessary  to  establish  a  system  of  stand- 
ards tp  which  these  measurements  can  be  referred.  Various 
systems  of  standards  have  been  devised;  they  differ  from 
one  another  principally  in  the  selection  of  their  fundamental 
units.  As  a  matter  of  fact,  however,  there  is  practically 
only  one  system  used  in  the  scientific  work  of  to-day.  This  is 
the  centimeter-gram-second  system,  the  C.G.S.  system,  as  it 
is  generally  termed  from  the  initial  letters  of  its  three  units 
of  space,  mass,  and  time. 

The  unit  of  length  adopted  in  this  system  is  the. centi- 
meter. This  is  the  one-hundredth  part  of  the  standard 
meter,  a  bar  made  of  an  alloy  consisting  of  90%  platinum 
and  of  10%  iridium.  This  standard  bar  is  preserved  by  the 
International  Bureau  of  Weights  and  Measures  in  Sevres, 
near  Paris,  France. 

The  unit  of  mass  *  of  the  C.G.S.  system  is  the  mass  of  one 

*  Conception  of  mass,  as  this  term  is  now  used,  is  due  to  Newton. 
A  clear  distinction  must  be  made  between  mass  and  weight.  The 
mass  of  a  body  is  invariable;  it  is  the  same  throughout  the  universe. 
The  weight  of  a  body  depends  on  gravitation:  on  the  earth,  for  in- 
stance, the  weight  of  a  body  measures  the  earth's  attraction  for  that 


6  NOTES  ON  ELECTROCHEMISTRY. 

cubic  centimeter  of  water  at  a  temperature  of  4°  Centigrade. 
It  is  represented  by  the  one-thousandth  part  of  the  Inter- 
national kilogram,  a  cylinder  made  of  the  same  alloy  of 
which  the  standard  meter  is  made;  it  also  is  preserved  by 
the  International  Bureau  of  Weights  and  Measures  in  France. 
Copies  of  these  International  standards  are  in  the  possession 
of  the  United  fcjtates  Government  at  Washington,  D.C. 

The  unit  of  time  of  the  C.G.S.  system  is  the  solar  second. 
This  is  the  ^iutf  part  of  a  mean  solar  day.  The  duration  of 
the  latter  is  of  course  determined  by  the  motion  of  the  earth 
with  respect  to  the  sun,  the  interval  between  successive 
transits  of  the  sun  over  the  meridian. 

All  of  the  fundamental  quantities  used  in  the  C.G.S.  system 
are  fixed  and  un variable;  and  as  definite  amounts  of  these 
quantities,  the  centimeter,  the  gram,  and  the  second,  have 
been  accepted,  this  C.G.S.  system  is  designated  as  an  abso- 
lute system  of  units. 

The  unit  of  velocity  adopted  in  this  system  is  one  centi- 
meter per  second.  The  unit  of  force,  that  force  which,  acting 
on  one  gram-mass  at  rest,  produces  in  one  second  a  velocity 
of  one  centimeter  per  second  —  this  is  called  a  dyne.  The 
unit  of  energy  is  the  erg:  an  erg  is  one  dyne  acting  through 
one  centimeter. 

The  units  of  all  forms  of  energy  can  be  referred  to  the  centi- 
meter, the  gram,  and  the  second.  In  the  measurement  of 
electrical  energy  there  are  two  C.G.S.  systems:  the  electro- 
static and  the  electromagnetic  system.  In  the  electro- 
static system  all  units  are  based  upon  the  force  exerted 
between  two  quantities  of  electricity  —  that  amount  of  elec- 
tricity which  attracts  or  repels  an  equal  amount  of  electricity 
one  centimeter  distant  with  the  force  of  one  dyne. 

body.  Weight,  however,  is-  the  most  convenient  measure  of  mass, 
and  consequently  these  two  terms  are  frequently,  though  errone- 
ously, considered  synonymous. 


GENERAL  PRINCIPLES.  7 

The  electromagnetic  system  is  based  upon  the  force  ex- 
erted between  an  electric  current  and  a  magnetic  pole.  In 
this  system  the  unit  current  of  electricity  is  defined  as  that 
current  which,  flowing  through  an  arc  of  one  centimeter, 
curved  to  a  radius  of  one  centimeter,  generates  a  unit  mag- 
netic pole  at  the  center..  The  electrical  units  in  common 
use  are  based  on  this  system. 


CHAPTER   II. 
ELECTRICAL   ENERGY. 

Literature:  DESCHANEL,  A.  P.,  and  EVERETT,  J.  D.:  "Natural  Phi- 
losophy." New  York,  1889.  HABER,  F.:  "Grundriss  der  Tech- 
nischen  Elektrochemie  auf  Theoretischer  Grundlage."  Miinchen, 
1898.  HERING,  C.:  "Ready  Reference  Tables,"  Vol.  I.  New 
York,  1904.  LE  BLANC,  M.  (English  translation  by  WHITNEY, 
W.  R.):  "Elements  of  Electrochemistry."  London,  1896.  RO- 
SENBERG, E.  (English  translation  by  SEE,  W.  W.  H.,  and  KINZ- 
BRUNNER,  C.):  "Electrical  Engineering."  New  York,  1903. 
RUTHERFORD,  E:  " Radio-Activity."  Cambridge,  1904.  SODDY, 
F. :  "Radio-Activity,  an  Elementary  Treatise,  from  the  Stand- 
point of  the  Disintegration  Theory."  New  York,  1904. 

Theories  of  Electricity.  —  The  word  "  electricity  "  is  derived 
from  the  Greek,  electron,  amber,  because  the  manifestation 
of  certain  electrical  properties — attraction,  repulsion  — 
was  originally  noted  in  amber.  Credit  for  having  been  the 
first  to  observe  these  phenomena  is  generally  given  to  Thales, 
who  lived  some  two  thousand  years  ago. 

Introduction  of  the  word  "  electricity  "  is  due  to  William 
Gilbert,  or  Gilberd  (1540-1603),  who  has  been  named  "  the 
creator  of  the  science  of  electricity."  His  principal  work, 
"  De  Magnete,  Magneticisque  Corporibus,  et  de  Magno  Mag- 
nete  Tellure,  Physiologia  Nova/'  published  in  1600,  is  re- 
plete with  interesting  facts  and  observations  of  magnetic 
phenomena. 

Since  the  days  of  Gilbert  innumerable  observations  of 
electrical  phenomena  have  been  made,  and  a  great  number 
of  data  bearing  on  them  have  been  recorded.  Still,  although 
so  much  is  known  of  the  properties  of  electricity,  and  al- 
though electricity  has  unquestionably  become  one  of  the 


ELECTRICAL  ENERGY.  D 

most  potent  agencies  in  the  advancement  of  human  welfare, 
the  true  nature  of  electricity  remains  as  yet  an  unsolved 
problem. 

At  various  times,  various  theories  have  been  advanced  in 
explanation  of  electrical  phenomena.  Thus,  Benjamin  Frank- 
lin (1706-1790)  suggested  the  one-fluid  theory  of  electricity. 
All  unelectrified  bodies  were  supposed  to  possess  a  normal 
amount  of  electricity;  a  positively  electrified  body  contained 
an  excess,  a  negatively  electrified  body,  a  deficiency  of  this 
electric  fluid. 

Franklin  was  the  one  to  introduce  the  terms  positive  and 
negative  electricity.  They  are  retained  to  this  day  as  con- 
ventional terms,  indicating  for  one  thing  forces  in  opposite 
directions,  —  for  instance,  the  direction  of  flow  of  electric 
currents. 

Dufaye,  in  1733,  originally  advanced  the  two-fluid  theory 
of  electricity;  it  was  more  precisely  formulated  by  Symmer. 
This  theory  holds  that  there  are  two  kinds  of  electricity  — 
positive  and  negative;  union  of  equal  amounts  of  the  two 
forms  the  neutral  fluid,  which  is  present  in  all  unelectrified 
bodies.  The  total  amount  of  electric  fluid  in  a  body  is  a 
constant  quantity;  additional  gain  of  the  one  kind  necessi- 
tates an  equivalent  loss  of  the  other.  Whenever  an  electric 
current  of  one  kind  flows  through  a  conductor  in  one  direc- 
tion, an  equivalent  amount  of  current  of  the  other  kind  flows 
in  the  opposite  direction. 

Both  of  these  "  fluid  "  theories  hold  in  common  that  the 
electricity  passing  along  a  conductor  —  the  electric  current 
—  is  continuous  in  character. 

Recent  studies,  however,  made  in  the  discharge  of  elec- 
tricity through  gases,  have  brought  about  a  decided  change 
of  view  concerning  the  nature  of  electricity. 

Such  discharges  of  electricity  through  gases  are  unquestion- 
ably convective.  Particles  charged  with  positive,  and  par- 
ticles charged  with  negative  electricity,  are  present  in  gases; 


10  NOTES  ON  ELECTROCHEMISTRY. 

these  particles,  ions,  which  term  signifies  wanderers,  can  be 
induced  in  gases  by  Rontgen  rays,  by  ultra-violet  light,  and 
by  other  means.  They  move  under  the  influence  of  elec- 
trical energy,  and  it  is  their  motion  which  constitutes  the 
electric  current. 

From  the  researches  of  J.  J.  Thomson  it  appears  that  the 
negatively  charged  particles  thus  present  in  a  gas  have  a 
mass  of  approximately  one  one-thousandth  that  of  a  hydrogen 
atom;  positively  charged  particles  of  similar  dimensions  are 
not  known. 

The  electron  theory,  the  theory  which  promises  to  become 
the  leading  theory  of  electricity  in  the  immediate  future,  is 
based  on  these  studies.  According  to  the  electron  theory 
there  exists  but  one  kind  of  electricity,  —  that  which  is  gen- 
erally designated  as  negative  electricity. 

This  negative  electricity  is  assumed  to  occur  in  definite 
unit  charges,  and  these  smallest  particles  of  electricity,  the 
atoms  of  electricity,  are  termed  electrons. 

The  term  "  electron  "  was  originally  given  by  G.  Johnstone 
Stoney  to  the  definite  charges  of  electricity  associated  with 
ions;  the  concept  of  electrons  as  separate,  distinct  individual 
particles  was  only  arrived  at  later.  However,  in  this  con- 
nection it  is  interesting  to  recall  that  W.  K.  Clifford,  as  early 
.as  1875,  made  the  following  statement:  "  There  is  great  reason 
to  believe  that  every  material  atom  carries  upon  it  a  small 
electric  current,  if  it  does  not  wholly  consist  of  this  current." 

In  a  substance  which  is  electrically  neutral,  the  electrons 
are  so  disposed  with  respect  to  the  balance  of  the  matter 
that  there  is  no  evidence  of  an  outside  electric  field. 

In  a  substance  which  bears  a  positive  charge  of  electricity, 
there  is  a  lack,  a  deficiency  of  electrons.  A  substance  which 
is  negatively  charged  has  an  excess  of  electrons.  As  Sir 
William  Crookes  has  expressed  it:  "  A  :so-called  negatively 
charged  chemical  atom  is  one  having  a  surplus  of  electrons, 
the  number  depending  on  ttie  valency,  whilst  a  positive  ion 


ELECTRICAL  ENERGY.  11 

is  one  having  a  deficiency  of  electrons.  Differences  of  elec- 
trical charge  may  thus  be  likened  to  debits  and  credits  in 
one's  banking  account,  the  electrons  acting  as  current  coin  of 
the  realm.  On  this  view  only  the  electron  exists;  it  is  the 
atom  of  electricity,  and  the  words  positive  and  negative, 
signifying  defect  and  excess  *  of  electrons,  are  only  used  for 
convenience  of  old-fashioned  nomenclature." 

Radio- Activity.  —  In  this  connection  reference  must  be 
had  to  the  subject  of  radio-activity,  a  theme  so  intimately 
concerned  with  the  theory  of  electrons,  and  of  vital  interest 
and  importance  on  account  of  the  far-reaching  influence  it 
is  exerting  on  the  present  trend  of  physical  science  in  par- 
ticular, and  of  scientific  thought  in  general. 

Discovery  of  the  X-rays  by  Ron tgen  (1895)  led  to  numer- 
ous researches  to  determine  whether  analogous  radiations 
might  not  be  given  out  by  other  substances.  Thus,  Bec- 
querel,  in  1896,  discovered  the  radio-activity  of  uranium; 
G.  C.  Schmidt,  in  1898,  that  of  thorium;  and  M.  and  Mme. 
Curie,  together  with  M.  Bemont,  also  in  the  year  last 
named,  isolated  the  new  element  radium  from  the  mineral 
pitchblende. 

Radium  gives  out  three  kinds  of  rays,  named  the  a-,  £-,  and 
y-rays. 

The  a-rays  are  material  particles  bearing  charges  of  posi- 
tive electricity.  They  have  a  mass  equal  to  about  twice  the 
mass  of  a  hydrogen  atom;  they  move  with  a  velocity  about 
one-tenth  that  of  light,  i.e.,  about  20,000  miles  per  second, 
and  are  readily  arrested  by  an  air-gap  of  a  few  centimeters, 
by  paper,  and  by  thin  layers  of  aluminium  foil.  The  lumi- 
nous phenomena  shown  by  the  spinthariscope  of  Sir  William 
Crookes  are  caused  by  the  impact  of  a-  particles  on  a  screen 
of  sulphide  of  zinc,  these  impacts  of  the  swiftly  moving  par- 

.*  In  -the  original,  Bericht  V.  Int.  Kong.  Ang.  Chem.  1903,  Vol.  I, 
p.  96,  the  words  "defect"  and  "excess"  are  printed  in  reverse 
order.  —  F.  G.  W. 


12  NOTES  OX  ELECTROCHEMISTRY. 

tides  evoking  the  flashes  which  make  the  screen  appear  a 
seething  sea  of  light. 

The  £-rays  are  in  all  probability  identical  with  the  cathode 
rays  which  appear  at  the  negative  electrode  of  a  vacuum 
tube  on  the  passing  of  an  electric  discharge.  These  /3-rays 
consist  of  negatively  charged  particles  having  a  mass  of 
approximately  one  one-thousandth  the  mass  of  a  hydrogen 
atom;  they  travel  with  a  velocity  approximating  to  that  of 
light.  The  minuteness  of  these  little  particles  will  be  appre- 
ciated from  a  comparison  made  by  Sir  William  Crookes,  who 
stated,  that  if  the  sun's  diameter  were  taken  to  be  about  one 
and  one-half  million  kilometers,  and  that  of  the  smallest  planet- 
oid about  twenty-four  kilometers,  that  then,  if  an  atom  of 
hydrogen  were  magnified  to  the  size  of  the  sun,  an  electron 
would  have  a  diameter  about  two-thirds  that  of  the  planetoid. 

The  )8-rays  are  the  chief  agents  in  the  photo-activity  of 
the  radium  rays.  Like  the  a-rays,  the  /?-rays  are  also  de- 
flected by  a  magnetic  field,  but  in  a  direction  opposite  to 
that  in  which  the  a-rays  are  turned. 

The  y-rays  are  more  penetrating  than  either  the  a-  or 
/3-rays.  They  are  not  deflected  by  an  electric  field,  and  thus 
far  no  proof  has  been  furnished  that  they  are  material  par- 
ticles; possibly  they  may  be  ethereal  vibrations  analogous  tor 
or  even  identical  with,  the  Rontgen  rays. 

Considered  as  a  whole,  radium  rays  exercise  certain  re- 
markable influences.  They  evoke  luminosity  in  some  sub- 
stances, in  sulphide  of  zinc,  for  instance,  and  in  diamonds; 
they  destroy  the  power  of  germination  in  seeds;  they  can 
extend  the  larvae  stage  of  some  insects,  and  can  cause  burns 
and  even  bring  death  to  living  organisms. 

The  property  which  radium  rays  possess  of  ionizing  dry 
air  and  other  gases,  that  is,  of  making  these  substances  con- 
ductors of  electricity,  is  taken  advantage  of  for  their  detec- 
tion and  for  the  measurement  of  the  strength  of  radium 
preparations.  This  determination  is  accomplished  by  bring- 


ELECTRICAL  ENERGY.  13 

ing  a  sealed  tube  containing  radium  into  the  neighborhood 
of  an  aluminium-foil  electroscope  placed  in  dry  air.  The 
radium  transforms  the  air,  which  is  normally  an  insulator, 
into  a  conductor,  and  this  enables  the  electric  charge  of  the 
electroscope  to  pass  away.  The  speed  with  which  this  dis- 
charge takes  place  allows  of  a  quantitative  estimation  of  the 
radio-activity  of  the  preparation. 

In  addition  to  the  three  kinds  of  rays  which  radium  emits, 
it  also  gives  off  an  emanation  which  is  more  radio-active  than 
radium  itself.  This  emanation  is  poisonous  to  animal  life, 
is  very  unstable,  slightly  soluble  in  water,  and  is  condensed 
at  a  temperature  of  —  150°  C.  to  —  155°  C. 

As  determined  by  Sir  William  Ramsay  and  Mr.  Soddy, 
this  emanation  has  been  found  to  yield  another  element  — 
helium  —  as  one  of  its  products  of  decomposition.  Appar- 
ently, radium  passes  through  six  other  stages  before  it  finally 
appears  in  the  form  of  helium,  which  is  not  radio-active. 
This  transformation  proceeds  undisturbed  by  changes  in  ex- 
ternal conditions,  such  as  changes  in  temperature,  light,  or  dark- 
ness. It  has  been  estimated  that  about  one  two-thousandth 
part  of  a  given  quantity  of  pure  radium  disintegrates  per 
annum.  The  change  of  radium  into  helium  is  thus  far  the 
only  authenticated  instance  known  of  a  transmutation  of 
one  element  into  another. 

Induced  radio-activity  is  caused  by  a  very  fine  film  of  a 
solid  substance  deposited  by  the  radium  emanation  on  sur- 
faces exposed  to  it.  This  film  may  be  mechanically  removed 
by  brushing  or  by  wiping  it  with  a  cloth;  if  left  undisturbed 
this  film  soon  loses  its  radio-activity. 

Radium  also  continuously  gives  out  energy  in  the  form  of 
heat.  One  gram  of  pure  radium  gives  out  about  100  calo- 
ries per  hour,  and  Rutherford  has  estimated  that  the  heat 
given  out  by  the  transformation  of  one  gram  of  radium  into 
helium  is  about  one  million  times  as  great  as  the  heat  given 
out  in  the  formation  of  one  gram  of  water. 


.14  NOTES  ON  ELECTROCHEMISTRY. 

An  interesting  hypothesis  to  account  for  the  usual  positive 
electrification  of  the  atmosphere  and  for  the  negative  electri- 
fication of  the  earth,  has  been  based  by  Professor  Ebert  on 
the  activity  of  radio-emanations.  He  holds  that  these  ema- 
nations in  passing  from  the  earth  into  the  atmosphere  impart 
their  negative  charge  to  the  capillaries  of  the  soil  through 
which  they  pass,  and  thus  enter  the  air  with  high  positive 
charges,  which  they  transmit  to  the  atmosphere. 

Factors  of  Electrical  Energy.  —  If  one  chooses  to  look  upon 
electricity  as  a  form  of  energy,  then  electricity,  like  all  other 
forms  of  energy,  may  be  viewed  as  the  product  of  two  fac- 
tors, —  an  intensity-factor  and  a  capacity-factor. 

The  intensity-factor  of  electrical  energy  is  termed  its  po- 
tential or  tension;  the  capacity-factor  represents  quantity  of 
electricity.  To  compare  electrical  with  thermal  energy,  for 
instance,  electric  potential  corresponds  to  the  temperature 
of  thermal  energy,  electric  capacity  corresponds  to  heat- 
capacity. 

Heat  always  passes  from  objects  of  a  higher  to  objects  of 
a  lower  temperature;  the  extent  of  heat-exchange  between 
two  points  of  unequal  temperatures  is  determined  solely  by 
the  difference  between  those  temperatures,  but  is  wholly 
independent  of  the  absolute  temperatures. 

In  a  similar  manner  the  passing  of  an  electric  current 
between  two  points  is  determined  by  the  difference  in 
tension-potential  between  those  points.  When  positive  elec- 
tricity passes  from  a  point  of  higher  to  a  lower  potential,  a 
corresponding  amount  of  negative  electricity  must  be  con- 
ceived of  as  passing  in  the  opposite  direction.  This  may,  in 
a  way,  be  regarded  as  analogous  to  the  conception  that  a 
given  amount  of  cold  is  raised  to  a  higher  temperature  when- 
ever an  equal  amount  of  heat  passes  from  a  higher  to  a  lower 
temperature. 

Properties  of  Electricity.  —  Electricity  may  be  conveyed 
from  one  location  to  another  either  by  means  of  conductors 


ELECTRICAL  ENERGY.  15 

in  which  there  is  no  evident,  simultaneous  movement  of  the 
matter  of  which  the  conductor  consists,  or  by  means  of  sub- 
stances in  which  a  transportation  of  material  particles  ac- 
companies the  transference  of  the  electric  charge.  Con- 
ductors of  the  former  kind  are  known  as  conductors  of  the 
first  class;  the  metals,  metallic  sulphides,  and  carbon  belong 
to  this  group.  Conductors  of  the  other  kind  are  called  con- 
ductors of  the  second  class;  to  these  belong  the  salts,  the 
acids  and  bases  when  in  solution,  and  salts  and  bases  also 
when  in  a  state  of  fusion. 

While  the  domain  of  electrochemistry  lies  essentially  with 
conductors  of  the  second  class,  for  the  moment  attention 
shall  be  given  to  the  phenomena  to  be  noted  when  a  current 
of  electricity  flows  along  a  conductor  of  the  first  class,  for 
instance,  along  a  metal  wire. 

If  a  plate  of  copper  and  a  plate  of  zinc  are  placed  in  a 
vessel  containing  dilute  sulphuric  acid,  and  the  two  metal 
plates  are  connected  by  a  metal  wire,  outside  of  the  fluid, 
observation  will  show  that  this  wire  soon  becomes  heated, 
and  if  a  break  is  made  anywhere  in  this  wire  so  that  an  air- 
gap  intervenes  between  the  two  ends  of  the  wire,  a  spark  of 
light  will  appear  the  instant  the  break  is  made. 

If  the  wire  remain  unbroken,  a  magnetic  needle  brought 
near  to  it  will  be  deflected  from  its  normal  position.  If  the 
wire  be  wound  around  a  bar  of  soft  iron,  the  iron  becomes 
magnetic,  and  remains  so  at  least  as  long  as  the  wire  encircles 
it.  If  the  wire  be  cut  or  broken  and  the  ends  inserted  in 
acidulated  water,  bubbles  will  arise  from  the  water,  and  the 
water  will  be  found  to  suffer  decomposition  into  its  compo- 
nent elements,  oxygen  and  hydrogen  gases. 

These  phenomena  make  evident  that  some  process  is  taking 
place  —  an  electric  current  is  passing  along  the  wire,  and 
the  phenomena  referred  to  establish  the  fact  that  an 
electric  current  can  induce  heating,  lighting,  magnetic  and 
chemical  effects. 


16  NOTES  ON  ELECTROCHEMISTRY. 

There  is  evidently  a  force  at  work  which  drives  the  electric 
current  along  the  wire.  If  we  use  two  galvanic  elements  in- 
stead of  one,  connecting  the  zinc-plate  of  element  No.  1  with 
the  copper-plate  of  element  No.  2,  and  then  lead  a  connecting 
wire  from  the  copper-plate  of  No.  1  to  the  zinc-plate  of  No.  2, 
a  much  stronger  current  will  be  secured  than  if  only  one 
element  had  been  used.  It  appears  that  the  pressure  driving 
the  electric  current  along  the  wire  has  been  increased.  The 
pressure  thus  forcing  the  current  along  the  wire  is  termed 
electromotive  force,  and  the  unit  in  terms  of  which  this  is 
measured  is  the  volt. 

The  International  volt  is  that  electromotive  force  which 
will  maintain  one  International  ampere  through  a  resistance 
of  one  International  ohm.  For  practical  purposes  it  is 
represented  by  1  -*-  1.434  of  that  of  a  Clark  cell  at  15°  C. 

The  cause  of  the  flow  of  the  electric  current  is,  as  has  been 
said,  a  difference  in  the  electrical  pressure,  a  difference  in 
electrical  potential  between  different  parts  of  the  circuit. 
Water  standing  in  two  connecting  vessels  will  remain  at  rest 
whenever  it  stands  at  the  same  level  in  both  vessels.  If, 
however,  there  is  a  difference  of  level  in  the  two  vessels,  then 
the  force  determined  by  the  difference  in  height  of  these 
levels  will  cause  a  current  of  water  to  flow  from  the  higher  to 
the  lower  level.  By  analogy  we  can  conceive  a  similar  dif- 
ference in  electric  pressure  to  be  the  cause  of  flow  of  an 
electric  current. 

The  rate  of  flow  of  an  electric  current  per  second  is  termed 
its  current  strength.  Current  strength,  or  current  intensity, 
as  it  is  also  called,  is  measured  in  amperes.  The  International 
ampere  is  the  current  which,  under  specified  conditions,  will 
•deposit  0.001118  gram  of  silver  per  second. 

Amperes  are  comparable  to  the  flow  of  water  measured 
in  some  unit  of  volume,  for  instance,  in  liters  or  in  cubic 
feet  per  second.  Thus,  a  flow  of  water  of  20  liters  per  second 
under  a  pressure  of  50  kilograms,  increases  to  a  flow  of  40 


ELECTRICAL  ENERGY.  17 

liters  per  second  under  a  pressure  of  100  kilograms.  In  an 
analogous  manner  an  electric  current  of  20  amperes  under 
an  electric  pressure  of  50  volts  is  changed  to  a  current  of  40 
amperes  under  a  pressure  of  100  volts.  Amperes  do  not 
.decrease  by  doing  work,  neither  does  a  volume  of  water 
grow  less  in  consequence  of  doing  work,  driving  a  turbine, 
for  instance;  the  work  done  is  in  direct  ratio  to  the  drop  in 
potential  or  pressure. 

In  passing  through  a  conductor,  the  electric  current  has  to 
overcome  the  resistance  in  its  path.  The  longer  the  con- 
ductor, a  wire,  for  instance,  and  the  smaller  its  cross-section, 
the  greater  is  the  resistance  to  be  overcome.  In  other 
words,  it  may  be  said  that  the  resistance  varies  directly  as 
the  length  and  inversely  as  the  cross-section  of  the  conductor 
along  which  a  current  flows. 

Resistance  is  measured  in  units  called  ohms.  The  Inter- 
national ohm  is  represented  by  the  resistance  of  a  column 
of  mercury  at  0°  C.  106.3  centimeters  long,  weighing  14.4521 
grams,  and  having  a  uniform  cross-section.  The  resistance 
met  by  an  electric  current  in  its  flow  is  directly  comparable 
to  the  friction  encountered  by  a  current  of  water  flowing 
through  a  pipe;  there,  too,  the  friction  varies  directly  with 
the  length  of  the  pipe  and  inversely  with  its  diameter. 

The  names  of  the  electrical  units  thus  far  considered  are 
derived  from  the  names  of  men  eminent  in  the  development 
of  electrical  science.  Thus,  the  volt  is  taken  from  the  name 
of  Alexander  Volta  (1745-1827),  the  ampere  from  that  of 
Andre  Marie  Ampere  (1775-1836),  the  ohm  from  that  of 
Georg  Simon  Ohm  (1789-1854). 

Ohm's  Law.  — There  is  an  intimate  relation  between  the 
electromotive  force,  the  current  strength,  and  the  resistance 
of  an  electric  current. 

If  these  terms  be  represented  by  their  initial  letters, 
thus: 


18  NOTES  ON  ELECTROCHEMISTRY. 

Current  strength  *=*  0,    fc« 

Electromotive  force  =  E, 

Resistance  =  R, 
•p 

the  expression  C  =  —  indicates  that  the   current  strength  is 
R 

equal  to  the  electromotive  force  divided  by  the  resistance. 

This  is  the  famous  law  of  Ohm,  the  discoverer  of  the 
relation  here  expressed;  it  is  a  law  of  fundamental  impor- 
tance in  electrical  science. 

By  transposition  we  have  : 


..,,  .       -§.  .....  ii 

E  =  CR, 

and  as  the  unit  of  current  strength  is  the  ampere,  that  of 
resistance  the  ohm,  and  that  of  electromotive  force  the  volt, 
these  formulae  express  that: 

Amperes  =  volts         -H  ohms, 
Ohms        =  volts         -s-  amperes, 
Volts         =  amperes    x  ohms. 

In  addition  to  the  units  discussed,  there  are  several  others 
which  are  frequently  used  in  considering  electrical  data. 

The  coulomb  is  the  unit  of  electrical  quantity;  the  word 
is  derived  from  the  name  of  Charles  Augustm  Coulomb 
(1736-1806).  The  International  coulomb  is  defined  as  the 
quantity  of  electricity  transferred  by  a  current  of  one  Inter- 
national ampere  in  one  second. 

Sometimes  the  quantity  of  electricity  transferred  by  a 
current  of  one  ampere  in  one  hour  is  employed  as  a  unit; 
this  is  called  an  ampere-hour,  and  is  a  unit  much  used  jn 
electrochemistrv. 


ELECTRICAL  ENERGY.  19 

The  farad,  derived  from  the  name  of  Michael  Faraday 
(1791-1867),  is  the  unit  of  electrical  capacity,  for  instance, 
of  a  condenser,  to  hold  electric  charges  under  electric  pres- 
sure or  stress.  The  capacity  in  farads  equals  the  charge  in 
coulombs  divided  by  the  electromotive  force  in  volts.  The 
unit  actually  used,  however,  for  measurements  of  electrical 
capacity,  is  the  microfarad,  one  one-millionth  of  a  farad. 

The  watt  is  the  unit  of  electrical  power;  the  name  com- 
memorates James  Watt  (1736-1819),  the  pioneer  of  modern 
steam-engineering.  The  power  in  watts  is  the  product  ob- 
tained by  multiplying  volts  and  amperes.  Representing 
power  by  P,  the  various  relations  between  power,  electro- 
motive force,  current  strength,  and  resistance  are  indicated 

by   the   formula?:    P  =  EC;    P  =  ~  ;     P  =  C2R.     The  de- 

H 

pendence  of  electric  power  on  both  current  strength  and 
voltage  is  evident  from  a  consideration  of  the  analogy  pre- 
viously introduced.  In  that  case,  it  will  be  recalled,  the 
work  effected  by  the  flowing  water  was  determined  by  both 
the  difference  in  height  between  the  two  water-levels  and  by 
the  amount  of  water  passed.  One  kilogram  of  water  flowing 
down  a  height  of  one  hundred  meters,  will  do  five  times 
the  work  that  is  done  by  one  kilogram  of  water  flowing  down 
a  height  of  twenty  meters.  .The  power  of  falling  water  is 
thus  measured  in  kilogrammeters  per  unit  of  time  (second  or 
minute) ;  75.0  kilogrammeters  per  second  are  one  metric  horse- 
power. The  flow  of  water  per  second  corresponds  to  the 
electric  current  strength;  the  water-pressure  due  to  the  dif- 
ference of  the  water-levels,  to  its  voltage.  Thus,  735:448 
watts  are  equal  to  one  metric  horse-power.  One  thousand 
watts  are  called  one  kilowatt,  and  are  equivalent  to  1.35972 
metric  horse-powers.* 

*  1  H.P.  =  76.0404  kg.-meters  per  second. 
1  H.P.  =  745,650  watts. 
1.34111  H.P.  =  1000  watts. 


20  NOTES  ON  ELECTROCHEMISTRY. 

The  unit  of  electrical  energy  or  work  is  the  joule.  The 
term  is  derived  from  the  name  of  James  Prescott  Joule 
(1818-1889),  who  practically  prepared  the  way  for  the  scien- 
tific study  of  thermodynamics. 

A  current  of  one  International  ampere  flowing  through  a 
resistance  of  one  International  ohm  for  one  second  does  one 
joule  of  work.  Joules  are  the  product  of  coulombs  and 
volts;  in  other  words,  joules  represent  watts  per  second. 

If  the  ampere-hour  is  taken  as  the  unit  of  electrical  quan- 
tity, the  corresponding  unit  of  electrical  energy  or  work  is 
the  volt-ampere-hour;  this  is  generally  designated  as  the 
watt-hour;  1000  watt-hours  are  termed  one  kilowatt-hour. 

The  relation  between  electrical  energy  and  heat  energy 
was  clearly  established  by  Joule,  in  1841.  This  relation  is 
expressed  in  the  following  law  which  bears  his  name:  "The 
heat  generated  in  the  whole  or  in  a  part  of  an  electric  circuit 
in  the  unit  of  time,  is  proportional  to  the  resistance  and  to 
the  square  of  the  current  strength." 

Experimental  study  has  shown  that  4.18617  (approxi- 
mately, 4.2)  watts  per  second  correspond  to  1  calorie  —  the 
calorie  being  defined  as  the  amount  of  heat  necessary  to  raise 
the  temperature  of  one  gram  of  water  from  15°  to  16°  hy- 
drogen scale.  This  is  regarded  as  equivalent  to  one  one- 
hundredth  of  the  amount  of  heat  that  will  raise  the  tempera- 
ture of  one  gram  of  water  from  0°  to  100°  C.  1-5-  4.18617 
=  0.238882;  therefore  0.238882  calorie  is  the  heat  equivalent 
of  one  joule,  and  this  means  that  one  joule  will  raise  the 
temperature  of  0.238882  gram  of  water  1°  C. 

The  unit  of  inductance  is  the  henry,  named  for  Joseph 
Henry  (1797-1878).  This  unit  is  used  in  measuring  the 
intensity  of  that  property  in  virtue  o-f  which  changes  of 
current  in  the  circuit  itself,  or  changes  of  current  in  an 
adjacent  circuit,  produce  electromotive  force.  The  henry  is 
the  quotient  obtained  by  dividing  induced  volts  by  rate  of 
change  of  amperes  per  second. 


ELECTRICAL  ENERGY.  21 

The  values  of  the  various  electrical  units  discussed  were 
fixed  by  an  International  Congress  of  Electricians,  which  met 
in  Chicago,  United  States  of  America,  in  1893. 

It  will  be  recalled  that  the  absolute  system  of  electrical 
units  used  is  electromagnetic  in  character;  that  is  to  say, 
that  the  units  in  that  system  are  based  upon  the  force  ex- 
erted between  an  electric  current  and  a  magnetic  pole.  As 
these  regular  C.G.S.  units  are,  however,  as  a  rule  either  too 
great  or  too  small  for  convenient  practical  use,  the  system 
of  practical  units,  which  has  just  been  so  fully  discussed, 
has  been  devised. 

These  practical  units,  as  they  are  called,  are  either  exact 
multiples  or  submultiples  of  the  absolute  C.G.S.  units  of  the 
electromagnetic  system.  The  following  table  shows  their 
relation : 

CORRESPONDS  TO 
UNIT  OF  :  NAME  :  C.G.S.,  UNITS  :  * 

Electromotive-force    .    .    .  Volt     ....    .    .    .    .  108 

Current  strength     ....  Ampere 10~' 

Resistance Ohm 108 

Quantity Coulomb      10~l 

Capacity Farad 10~8 

Power Watt 107  erg  per  second 

Energy  or  Work Joule 107  erg 

Inductance Henry 10* 

*  In  index-notation  a  positive  exponent  indicates  an  integral 
number;  thus,  102=100,  103  =  1000,  etc.  A  negative  exponent  de- 
notes the  reciprocal  of  the  indicated  power  of  10;  thus,  10~3=0.01, 
10-3  =0.001,  etc.  .  .  . 


CHAPTER   III. 

:-;v    i..;  ;   •   ,  ,:j  . '' .  ..."      'P'i^     ;:-v^v; 

ELECTROCHEMISTRY. 

Literature:  FERCHLAND,  P.:  "Grundriss  der  reinen  und  angewandten 
Elektrochemie."  HALLE,  A.  S.  1903.  HABER,  F.:  "Grundriss 
der  Technischen  Elektrochemie  auf  Theoretischer  Grundlage." 
Leipzig,  1898.  JONES,  H.  C.:  "Elements  of  Physical  Chemistry." 
New  York,  1902.  JONES,  H.  C.:  "Outlines  of  Electrochemistry." 
New  York,  1901.  LE  BLANC,  M.  (English  translation  by  WHIT- 
NEY, W.  R.):  "The  Elements  of  Electrochemistry."  London, 
1896.  LE  BLANC,  M.:  "Lehrbuch  der  Elektrochemie."  Leipzig, 
1903.  LEHFELDT,  R.  A.:  "Electrochemistry,"  Part  I,  General 
Theory.  New  York,  1904.  OSTWALD,  W.:  "Elektrochemie,  ihre 
Geschichte  und  Lehre."  Leipzig,  1896.  WIECHMANN,  F.  G.:  "Lec- 
ture-notes on  Theoretical  Chemistry."  New  York,  1895. 

Evolution  of  Electrochemistry.  —  Electrochemistry  is  the 
study  of  the  mutual  relation  and  transmutation  of  electrical 
and  chemical  energy.  It  deals  with  electrical  phenomena 
which  are  caused  by  chemical  reactions,  and  with  chemical 
changes  which  result  from  the  application  of  electrical  energy. 

Perhaps  the  earliest  instance  on  record  of  the  bringing 
about  of  chemical  change  by  electricity  is  the  reduction  of 
metallic  zinc  and  mercury  from  their  respective  oxides  by 
Beccaria,  about  the  seventh  decade  of  the  eighteenth  century, 
who  achieved  his  results  by  sparking  the  oxides  of  the  metals 
named  by  discharges  from  Leyden  jars. 

In  1775  John  Priestley  discovered  that  electric  sparks 
passing  through  air  acidify  the  air.  Priestley  believed  that 
the  acid  produced  was  carbonic  acid,  but  Cavendish,  repeat- 
ing the  experiments  of  Priestley,  showed  that  nitrous  and 
nitric  acids  were  formed. 

Ten  years  later  Van  Marum  in  Rotterdam,  subjected  many 


ELECTROCHEMISTRY.  23 

gases  and  metallic  substances  to  the  discharges  of  a  power- 
ful electrical  friction  machine,  and  among  other  chemical 
changes  which  he  thus  effected  was  the  decomposition  of 
"alkaline  air"  (ammonia)  into  its  components,  nitrogen  and 
hydrogen. 

Electrolytic  decomposition  of  water  into  "combustible 
air  "  (hydrogen)  arid  "  life  air"  (oxygen)  was  accomplished, 
in  1789,  by  Paets  van  Troostwijk,  Deimann,  and  Cuthbert- 
son.  Their  experiments  were  most  carefully  made  with 
distilled  water  and  with  water  from  which  the  absorbed  air 
had  been  removed  under  vacuum;  they  thus  proved  the 
belief  that  water  consists  of  hydrogen  and  oxygen  gases  to 
be  well  founded. 

The  speculations  which  were  indulged  in  at  that  time 
regarding  the  nature  of  electricity  are  interesting.  By 
some,  electricity  was  held  to,  be  a  substance  dual  in  its  char- 
acter, which  entered  into  union  with  the  elemental  constit- 
uents of  the  compounds  decomposed  by  its  influence;  others 
believed  it  to  be  a  highly  concentrated  form  of  fire  and  ac- 
counted for  its  great  powers  on  that  supposition. 

The  experiments  so  far  referred  to,  all  relate  to  the 
production  of  chemical  effects  by  the  agency  of  electrical 
energy.  The  first  attempt  recorded  to  produce  electrical 
phenomena  by  chemical  agencies  is  the  experiment  made  by 
Alessandro  Volta,  Lavoisier,  and  De  Laplace,  which  con- 
sisted in  electrifying  an  isolated  metallic  plate  by  placing 
on  it,  respectively,  basins  with  burning  charcoal  and  dishes 
in  which  sulphuric  acid  was  poured  over  iron  filings. 

About  the  same  time,  in  1782,  these  investigators  at- 
tempted, although  with  but  indifferent  success,  to  generate 
electricity  by  the  evaporation  of  water  and  the  subsequent 
condensation  of  the  vapor,  Volta  having  been  led  to  the 
conception  of  this  idea  through  his  studies  of  atmospheric 
electricity,  in  which  he  had  noticed  indications  of  the  presence 
of  electric  charges  in  rain  and  in  fog.  •< -\&iu\... 


24  XOTES  ON  ELECTROCHEMISTRY. 

An  incidental  observation  made  during  some  physiological 
experiments  led  Aloysius  Galvani,  professor  at  the  University 
of  Bologna,  in  1791,  to  the  discovery  of  a  form  of  electricity 
until  then  unknown;  he  styled  lit  animal  electricity,  conclud- 
ing that  the  electricity  thus  made  manifest  in  his  experi- 
ments was  produced  by  the  brain  of  the  animals  on  which 
he  worked,  and  that  the  electricity  thus  segregated  from 
the  blood  passed  through  the  nerve-channels  into  the  muscles, 
these  being  practically  a  kind  of  Ley  den  jar. 

Volta,  although  he  originally  shared  the  views  of  Galvani, 
was  gradually  led  to  abandon  the  supposed  biological  origin 
of  these  electrical  manifestations,  and  ultimately  showed 
their  origin  to  lie  in  the  contact  of  two  dissimilar  metals. 
This  discovery  led  him  to  establish  the  contact  theory  of 
electricity,  1792-1793,  which  held  sway  for  many  years. 

In  1800  Volta  published  an  account  of  the  voltaic  pile, 
which  made  it  possible  to  produce  galvanic  electricity  - 
"metallic  electricity,"  as  Volta  termed  it  —  in  sufficient 
quantity  and  of  sufficiently  high  potential  to  permit  of  a 
study  of  chemical  actions  induced  by  the  electric  current. 
The  beginning  of  electrochemistry  proper  may,  therefore,  be 
said  to  date  from  the  invention  of  the  voltaic  pile,  although 
it  should  not  be  forgotten  that  Professor  Fabroni,  of  Florence, 
in  1792,  had  suggested  chemical  action  to  be  "  the  nature  of 
the  new  stimulus,"  in  speaking  of  electricity  evoked  by  the 
immersion  of  metals  in  water. 

In  1800,  the  same  year  in  which  Volta  announced  the 
construction  of  the  voltaic  pile,  Carlisle  and  Nicholson 
effected  the  electrolytic  decomposition  of  water  by  means  of 
such  a  pile,  an  experiment  which,  it  will  be  recalled,  had 
already  been  made  by  the  aid  of  frictional  electricity  in  1789. 
Carlisle  and  Nicholson  also  noticed  the  chemical  reactions 
taking  place  within  the  voltaic  pile  itself.  A  little  later  Dr. 
Henry,  of  Manchester,  England,  effected  the  electrolytic  decom- 
position of  ammonia,  of  nitric  acid,  and  of  sulphuric  acid. 


ELECTROCHEMISTRY.  25 

Dr.  Wollaston,  in  1801,  ascertained  that  silver  can  be 
electrolytically  plated  with  copper,  if  the  silver,  in  connection 
with  some  metal  more  positive  than  itself,  is  immersed  in  a 
solution  of  a  copper  salt.  In  1803  Berzelius  and  Kissinger 
effected  the  electrolytic  decomposition  of  water  and  of  some 
neutral  salts,  while  about  the  same  time  Cruickshank  sug- 
gested the  use  of  the  electric  current  for  the  analysis  of 
minerals,  he  having  observed  the  electro-deposition  of  silver, 
copper,  and  lead  from  some  of  their  respective  salts.  In 
1805  the  electro-deposition  of  gold  on  silver,  and  the  electro- 
deposition  of  zinc  were  discovered  by  Brugnatelli. 

In  this  same  year  Von  Grothuss  offered  an  explanation  to 
account  for  the  electrolytic  decomposition  of  water.  At  the 
instant  of  such  decomposition  of  a  molecule  of  water,  the 
hydrogen  is  charged  electropositively  and  the  oxygen  electro- 
negatively.  The  former  is  repelled  from  the  positive  pole 
and  is  attracted  to  the  negative  pole;  the  oxygen  is  repelled 
from  the  negative,  and  is  attracted  to  the  positive  pole. 
The  initial  work  the  electricity  was  supposed  to  perform 
was  decomposition  of  the  water  molecules.  This  had  to  be 
done  ere  electrolysis  could  be  effected.  When  the  electric 
current  had  entered  the  water,  the  hydrogen  atom  adjacent 
to  the  negative  pole  gave  up  its  charge  to  that  pole,  and, 
having  become  electrically  neutral,  separated  in  the  form  of 
hydrogen  gas.  The  oxygen  atom  which  had  been  in  union 
with  this  atom,  combined  with  the  hydrogen  atom  of  the 
next  water  molecule,  and  thus  the  impulse  passed  along 
until  the  last  oxygen  atom,  in  contact  with  the  positive 
pole,  had  its  charge  neutralized  by  the  charge  of  this  pole, 
and  then  escaped  as  oxygen  gas. 

The  first  decade  of  the  nineteenth  century  also  witnessed 
the  separation  of  several  of  the  alkali  metals  from  their 
hydrates,  by  Sir  Humphrey  Davy;  thus,  potassium  and 
sodium  were  first  obtained  by  him  in  this  manner  in  October, 
1807. 


26  NOTES  ON  ELECTROCHEMISTRY. 

Led  thereto  by  the  results  of  his  experiments,  Davy  ad- 
vanced his  electrochemical  theory,  probably  the  first  theory 
of  its  kind  ever  formulated ;  it  rests  upon  the  atomic  hypoth-^ 
esis  of  Dalton.  According  to  its  teaching,  the  atoms  of 
substances  as  such  bear  no  electric  charges,  but  they  acquire 
positive  or  negative  charges  by  contact  with  each  other. 
Chemical  affinity  is  caused  by  and  depends  on  the  attraction 
of  such  opposite  electrical  charges.  Electrolytic  decomposi- 
tion is  effected  by  the  neutralization  of  these  charges. 

This  theory  of  Davy's  met  with  considerable  opposition, 
and  was  soon  displaced  by  the  views  advanced  by  Berzelius, 
outlined  in  1812  and  published  in  detail  two  years  later. 

Berzelius  held  that  every  atom  was  charged  with  both 
positive  and  negative  electricity,  and  that  the  electrical 
behavior  of  the  atom  depended  upon  whichever  of  these 
charges  was  present  in  excess.  Chemical  attraction  was  also 
ascribed  to  electrical  attraction  between  opposite  charges; 
the  one  or  the  other  of  these  predominated,  and  in  accord- 
ance therewith  the  resultant  compound  Exhibited  either  an 
electropositive  or  an  electronegative  character. 

Objections  to  this  theory  of  Berzelius  were,  however,  not 
lacking.  It  was  held  that  if  the  electrical  charges  of  the 
atoms  determined  chemical  union,  that  then  the  properties 
of  a  compound  must  be  a  function  of  those  charges.  The 
fact  that  three  atoms  of  chlorine  (electronegative)  could  be 
put  in  the  place  of  three  atoms  of  hydrogen  (electropositive) 
of  the  methyl  group  in  acetic  acid  without  causing  a  funda- 
mental disturbance  of  the  nature  of  the  compound,  was  an 
obstinate  fact  which  Berzelius  could  not  account  for. 

It  remained  for  J.  J.  Thomson,  in  1895,  to  show  that  an 
element  may,  according  to  circumstances,  bear  either  an 
electropositive  or  an  electronegative  charge,  and  that  "  it 
would  appear  that  the  chlorine  atoms,  in  the  chlorine  deriv- 
atives of  methane,  are  charged  with  electricity  of  the  same 
kind  as  the  hydrogen  atoms  they  displace.'* 


ELECTROCHEMISTRY,  27 

The  brilliant  -work  and  discoveries  of  Michael  Faraday, 
beginning  in  1832,  mark  the  next  important  epoch  in  the 
history  of  electrochemistry. 

Faraday  first  determined  the  identity  of  electricity  pro- 
duced by  friction  and  by  the  voltaic  pile.  When  he  had 
established  this,  he  turned  his  attention  to  the  relation  be- 
tween  the  amount  of  electricity  passing  through  a  circuit 
and  its  magnetic  and  chemical  effects,  and  found  that  the 
amount  of  chemical  decomposition  produced  in  an  electrolyte 
is  proportionate  to  the  amount  of  electricity  which  passes 
through  the  electrolyte. 

Faraday  further  studied  the  relation  between  the  amounts 
of  different  elements  set  free  from  their  compounds  on  pass- 
ing a  given  electric  current  through  solutions  of  these  com- 
pounds. Among  the  substances  which  he  investigated  in 
this  manner  were  solutions  of  some  salts  of  copper,  of  silver, 
and  of  zinc.  He  thus  determined  that  the  amounts  of  differ- 
ent elements  separated  by  the  same  quantity  of  electricity, 
stand  in  the  same  relation  to  each  other  as  the  chemical 
equivalents  *  of  those  elements.  This  means  that  all  mono- 
valent  atoms  bear  the  same  amount  of  electricity,  and  that  all 
multivalent  atoms  bear  some  simple  multiple  of  this  amount. 

It  must  be  especially  noted  that  these  laws  of  Faraday 
emphasize  the  fact  that  equal  quantities  of  electricity  sepa- 
rate chemically  equivalent  amounts  of  the  elements;  the 
electromotive  force,  the  potential  necessary  to  effect  this, 
is  not  referred  to  at  all;  this  factor  has  different  values 
with  different  electrolytes,  as  will  be  discussed  later. 

In  1857  Clausius  pointed  out  the  shortcomings  of  the 
theory  advanced  by  Grothuss,  and  suggested  that  solutions 
of  an  electrolyte  must  contain  some  part-molecules  in  addi- 
tion to  non-decomposed,  entire  molecules.  This  hypothesis 
offered  an  explanation  of  the  fact  that  even  very  weak 

*  The  chemical  equivalent  of  an  element  is  the  atomic  muss  of  that 
element  divided  bv  its  valence. 


28  .\OTES  ON   ELECTROCHEMISTRY. 

currents,  in  some  instances,  can  effect  electrolysis,  the  cur- 
rent exercising  a  directing  influence  on  the  part-molecules 
originally  present.  This  work  of  Clausius  practically  pre- 
pared the  way  for  the  theory  of  electrolytic  dissociation, 
which  was  brought  out  thirty  years  later. 

It  was  in  1887  that  J.  H.  Van't  Hoff  published  his  valuable 
article  on  the  role  which  osmotic  pressure  plays  in  solutions. 
This  paper,  in  the  same  year,  inspired  the  hypothesis  of 
Planck,  based  on  thermodynamical  considerations,  and  the 
theory  of  electrolytic  dissociation  advanced  by  Svante 
Arrhenius,  who  was  able  to  furnish  experimental  proof  of 
the  truth  of  Planck's  assumptions,  and  who  thus  established 
the  famous  theory  which  to-day  holds  the  leading  place  in 
electrochemical  science.  This  theory  will  later  be  con- 
sidered in  detail. 

Electrolysis.  —  Conductors  of  electricity  in  which  substance- 
movement  of  the  conducting  material  accompanies  the  pass- 
ing of  the  electric  current,  have  been  termed  conductors  of 
the  second  class.  In  this  category  are  included  all  solutions 
which  can  conduct  an  electric  current,  and  also  all  fused 
salts  which  can  act  as  conductors.  They  are  all  designated 
by  the  term  electrolytes,  and  the  particles  into  which  mole- 
cules of  electrolytes  dissociate  are  termed  ions. 

These  ions  are  particles  of  matter  associated  with  definite 
charges  of  electricity.  As  Von  Helmholtz,  in  his  Faraday 
lecture  delivered  in  London  in  1881,  expressed  it:  "If  we 
accept  the  hypothesis  that  the  elementary  substances  are 
composed  of  atoms,  we  cannot  avoid  concluding  that  elec- 
tricity also,  positive  as  well  as  negative,  is  divided  into 
definite  elementary  portions,  which  behave  like  atoms  of 
electricity.  As  long  as  it  moves  about  in  the  electrolytic 
fluid,  each  ion  remains  united  with  its  electric  equivalent, 
or  equivalents." 

The  terminals  of  the  wires  by  which  the  electric  current 
enters  and  leaves  the  electrolyte  are  called  electrodes;  the 


ELEC  TROCHEMISTRY.  29 

^electrode  by  which  the  current  enters  the  electrolyte  is  the 
anode;  the  one  by  which  it  leaves,  the  cathode.  The  ions, 
charged  with  positive  electricity,  which  are  discharged  at 
the  cathode,  are  termed  cathions;  the  negatively  charged 
ions  which  are  set  free  at  the  anode  are  called  anions.  The 
direction  of  current  flow  is  understood  to  be  the  direction 
•of  the  current  from  its  point  of  entry  into  the  electrolyte,  at 
the  anode,  across  the  electrolyte,  to,  and  emerging  at,  the 
cathode. 

The  distinguishing  feature  of  electrolysis  is  that  the  prod- 
ucts of  the  reaction  appear  only  at  the  electrodes.  It  was 
Faraday  who  studied  these  questions  of  electrolytic  phenom- 
ena with  the  utmost  care,  and  who  formulated  the  laws  which 
govern  these  reactions.  These  laws  have  been  previously 
referred  to;  they  may  be  concisely  expressed  as  follows: 

1.  The  amount  of  a  substance  set  free  or  deposited  by  an 
electric  current  is  proportional  to  the  quantity  of  electricity 
passing  through  the  electrolyte. 

2.  The  amounts  of  different  substances  separated  by  the 
same  quantity  of  electricity  bear  the  same  relation  to  each 
other  as  the  chemical  equivalent  weights  of  those  substances. 

The  most  rigid  experimental  tests  to  which  Faraday's  laws 
have  been  subjected,  on  the  one  hand  by  the  use  of  very 
large  currents  of  electricity  (Buff,  1853),  on  the  other  hand 
by  the  use  of  very  small  electric  currents  (Ostwald  and  Nernst, 
1889),  as  well  as  the  most  careful  determinations  of  electro- 
chemical equivalents,  which  have  been  made  by  many 
investigators,  have,  one  and  all,  only  served  to  demonstrate 
the  exactness  of  these  laws  of  Faraday. 

The  quantity  of  electricity  which  is  passing  through  an 
electrolyte  is  conveniently  ascertained  by  measuring  either 
the  weight  or  the  volume  of  the  products  resulting  from  its 
electrolytic  action. 

Apparatus  designed  for  this  purpose  are  generally  called 
-voltameters,  or  coulometers,  a  name  suggested  by  Professor 


30  NOTES  ON  E&BGTROCHEM1STRY. 

Richards,  in  1902,  to  avoid  confusing  voltameters  with  volt- 
meters. Various  forms  of  coulorneters  are  used;  the  most 
accurate  instrument  of  the  kind  is  probably  the  silver  cqulo- 
meter  in  which  metallic  silver  is  precipitated  on  the  cathode 
from  a  neutral  solution  of  nitrate  of  silver,  the  anode  con- 
sisting of  a  bar  of  pure  silver. 

Copper  and  mercury  coulometers  of  analogous  construction 
are  also  frequently  employed.  In  the  former,  both  electrodes 
are  of  metallic  copper  and  the  electrolyte  is  some  salt  of 
copper,  generally  sulphate  of  copper.  In  the  mercury  eoulo- 
meter  some  rnercurous  salt  is  used  as  the  electrolyte,  mer- 
curous  nitrate,  for  instance.  Both  anode  and  cathode  consist 
of  metallic  mercury  in  glass  receptacles. 

Another  favorite  form  of  coulometer  is  that  in  which 
the  electrolytic  decomposition  of  water  is  effected  and 
in  which  the  volume  of  the  resulting  gases  is  measured. 
These  gases,  hydrogen  and  oxygen,  may  be  caught  either 
separately  or  together,  and  their  volume  measured.  One 
ampere  in  one  minute  sets  free  10.45  C.  C.  of  these  mixed 
gases,  measured  at  0°  C.  and  760  mm.  pressure.  In  these 
gas  coulometers  a  solution  of  sodium  hydrate  or  dilute 
sulphuric  acid  is  generally  used;  if  the  former,  the  electrodes 
are  preferably  made  of  nickel;  if  sulphuric  acid  be  employed 
as  the  electrolyte,  the  electrodes  are  both  made  of  platinum. 

As  the  quantity  of  electricity  passing  through  any  given 
conductor  is  determined  by  the  current  strength,  measured 
in  amperes,  and  the  time  during  which  the  current  flows,  an 
identical  quantity  of  current  will  flow  and  an  identical 
amount  of  work,  electrolytic  or  other,  will  result,  whether, 
for  instance,  100  amperes  flow  for  5  seconds,  or  whether  250 
amperes  flow  for  2  seconds.  It  will  be  recalled  that  [the 
amount  of  electricity  conveyed  by  one  ampere  in  one  second 
is  termed  a  coulomb,  and  that  this  is  t he < quantity  of  elec- 
tricity which  will  deposit  0.001118  gram  of  silver  in  a-S;i}yer 
coulometer.  ?:•*»•;,  wter.rj|.?." 


ELECTROCHEMISTRY.  K  31 

This  amount,  0.001118  gram,  is  termed  the  ^electrochemical 
equivalent  of  silver.  This  term  must  be  well  distinguished 
from  the  expression  chemical  equivalent  or  equivalent .-weight, 
as  it  is  also  called.  The  latter,  it  will  be  remembered,  is  the 
quotient  obtained  on  dividing  the  atomic  weight  of  an  ele- 
ment by  its  valency.  Elements  whose  valency  is  oner  the 
so-called  monads,  have  their  chemical  equivalent  identical 
with  their  atomic  weight.  Elements  whose  valency  is  two, 
dyads,  have  their  chemical  equivalent  equal  to  one-half  their 
atomic  weight;  in  triads/it  is  one-third  the  atomic  weight, 
etc.  In  the  case  of  complex  ions  the  equivalent  weight  is 
equal  to  the  molecular  weight  —  that  is,  the  sum  of  the 
atomic  weights  of  the  complex  ion,  divided  by  its  valency. 

Application  of  Faraday's  second  law,  of  course,  makes  it 
a  simple  matter  to  calculate  the  electrochemical  equivalent 
of  every  element  when  the  electrochemical  equivalent  of 
any  one  element  has  been  accurately  determined  experi- 
mentally. 

To  illustrate,  let  a  determination  of  the  electrochemical 
equivalent  of  zinc  be  required. 

The  atomic  weight  of  zinc  is  65.4,  its  valency  is  2,  and  con- 
sequently its  equivalent  weight  is  65.4  -4-  2  =  32.7.  Accept- 
ing the  atomic  weight  of  silver  as  107.93  and  its  valency  as 
one,  that  quantity  of  electricity  which  will  deposit  0.001118- 
gram  of  silver  must  deposit  of  zinc: 

107.93  :  32.7  ::  0.001118  :x 
x  =  0.0003387  gram. 

This  value  is    therefore    the   electrochemical    equivalent  of 
zinc.* 

The  chemical  equivalent  weight  of  a  substance  in  grams 
is  termed  a  gram  equivalent  of  that  substance.  To  deposit 

*An  excellent  table  of  "•  Electrochemical  Equivalents  and  their  Deriva- 
tives," by  Carl  Hering,  M.E.,  is  published  in  Electrochemical  Industry, 
New  York,  January,  1903.  „-;:: 


32  NOTES  ON  ELECTROCHEMISTRY. 

one  gram  equivalent  of  any  element  requires  an  amount  of 
electricity,  in  coulombs,  equal  to  the  chemical  equivalent  of 
that  element  divided  by  its  electrochemical  equivalent. 

Thus,  to  deposit  one  gram  equivalent  of  silver  requires 
107.93  -H  .001118  =  96,538  coulombs.  This  value  varies 
slightly  with  different  experimenters.  The  electrochemical 
equivalent  of  silver  was  found' to  be: 

0.0011179  by  Lord  Rayleigh  and  Mrs.  Sedgewick, 
0.0011183  by  W.  and  F.  Kohlrausch, 
0.0011172  by  Richards,  Collins,  and  Heimwood, 
0.0011192  by  Patterson  and  Guthe, 
0.0011193  by  Kahle. 

Accepting  the  atomic  weight,  and  hence,  of  course,  the 
chemical  equivalent  of  silver,  as  107.93,  and  employing  the 
several  electrochemical  equivalents  above  given,  the  deter- 
mination by: 

Lord  Rayleigh  and  Mrs.  Sedgewick  =  96,547  coulombs, 
W.  and  F.  Kohlrausch  =  96,513  coulombs, 

Richards,  Collins,  and  Heimwood     =  96,608  coulombs, 
Patterson  and  Guthe  =  96,435  coulombs, 

Kahle  =  96,426  coulombs. 

We  will  accept  the  value  96,540  coulombs  as  the  ionic  charge 
for  a  monovalent  gram  ion,  this  being  the  value  usually 
employed. 

It  can  be  readily  shown  that  96,540  coulombs  are  required 
to  deposit  or  to  liberate  one  gram  equivalent  of  any  element, 
and  this  quantity  of  electricity,  viz:  96,540  coulombs  is  called 
a  faraday.  This  constant  is  of  the  greatest  importance  in 
electrochemical  work,  for  on  passing  one  faraday  through 
an  electrolyte  there  is  always  set  free  one  gram  equivalent 
of  an  ion  at  the  cathode,  and  one  gram  equivalent  of  an 
ion  at  the  anode,  provided  that  the  electrolysis  effected  is 
simple  and  not  complex. 


ELECTROCHEMISTRY.  33 

If  complex,  that  is,  if  more  than  one  kind  of  ion  is  set 
free  at  one  of  the  electrodes,  the  sum  total  of  the  ions  thus 
set  free  at  that  electrode  amounts  to  one  gram  equivalent. 
Thus,  in  the  electrolysis  of  water  one  faraday  causes  the 
liberation  of  1.008  grams  of  hydrogen  at  the  cathode  and  of 
8.000  grams  of  oxygen  at  the  anode.  If,  however,  in  the 
electro-analysis  of  an  alloy  two  metals  were  to  be  simul- 
taneously deposited  on  the  cathode,  then  the  sum  of  the  gram 
equivalents  of  these  two  metals  so  deposited  would  corre- 
spond to  the  work  done  by  one  faraday. 

Taking  the  chemical  equivalent  of  hydrogen  as  unity,  one 
coulomb  will  liberate 

107.93:1::.  001118:z 
x  =  0.00001036  gram  of  hydrogen. 

This  value,  which  was  determined  by  Lord  Rayleigh  as 
0.000010352  gram,  and  by  Kohlrausch  as  0.000010354  gram, 
is  the  electrochemical  equivalent  of  hydrogen.  The  chemical 
equivalent  of  any  element  multiplied  by  the  electrochemical 
equivalent  of  hydrogen  is,  of  course,  the  electrochemical 
equivalent  of  that  element. 

Designating  the  chemical  equivalent  of  any  element  by 
Z,  the  actual  weight  in  grams  of  such  element  deposited 
by  electrolysis  is  calculated  by  the  formula: 

w  =  0.00001036  Zct, 
in  which, 

w  =  weight  in  grams, 

Z  —  chemical  equivalent  of  the  element  deposited, 
c  =  current  strength  employed  (in  amperes), 
t  =  time  oT  passing  of  current  (in  seconds). 

Or,  designating  the  electrochemical  equivalent  of  the  ele- 
ment deposited  by  z,  this  formula  becomes: 

w  =  zct. 


OF  THF 

UNIVERSITY 

OF 
'FOR! 


34  NOTES  ON  ELECTROCHEMISTRY. 

If  the  time  be  measured  not  in  seconds  but  in  hours  T, 
then  cT  represents  ampere-hours,  that  is  to  say,  the  quan- 
tity of  electricity  conveyed  by  the  current  in  one  hour,  and 
the  formula  first  given  would  read: 

w  =     .00001036  X  3600  ZcT, 
w  =  0.037296  ZcT, 
or,  for  all  practical  purposes, 
10  -  0.0373  ZcT. 

From  this  formula  the  amount  of  current,  C.  is  readily  de- 
duced which  is  required  to  set  free  or  to  deposit  a  given 
weight  of  an  element,  w,  in  a  given  time: 

[1.0  -*-  .0373]  w 
~ZT~ 

26.81  w 


The  electrical  power,   in   watts,  needed  to  do  this  work  is 
calculated  by  the  formula: 

26. 


in  which  E  represents  the  electromotive  force,  the  voltago, 
employed. 

At  times  the  actual  amount  of  chemical  action  obtained 
—  take,  for  instance,  the  weight  of  a  metal  which  should  be 
deposited  in  an  electrochemical  process  —  does  not  corre- 
spond with  the  amount  called  for  by  Faraday's  laws. 

There  is  some  diversity  of  opinion  concerning  the  causes 
of  such  discrepancies.  Professor  Crocker*  attributes  the  dif- 
ficulty, in  some  instances,  to  the  liberation  of  hydrogen  gas 
in  place  of  the  metal  which  should  be  deposited;  this  setting 
free  of  the  hydrogen  may  be  due  to  an  excessive  current 

*  "School  of  Mines  Quarterly,"  Vol.  22,  p.  119. 


ELECTROCHEMISTRY.  35 

density,  to  too  great  a  dilution  of  the  electrolyte,  or  to  the 
great  affinity  which  some  metals  have  for  oxygen,  the  con- 
sequent decomposition  of  the  water  resulting  in  a  liberation 
of  hydrogen.  An  insufficient  yield  of  metal  may  also  be 
due  to  a  resolution  of  some  of  the  metal  by  free  acid,  such 
acid  being  sometimes  added  in  order  to  improve  the  con- 
ductivity of  an  electrolyte.  But  whatever  the  cause,  if  a 
discrepancy  exist  between  the  output  actually  obtained  and 
the  theoretical  yield  correctly  figured  according  to  Faraday's 
laws,  the  fault  of  such  discrepancy  will  be  found  not  to  rest 
with  the  latter. 

Electromotive  Force.  —  Electrical  energy  has  been  denned 
as  the  product  of  two  factors,  quantity  and  intensity  of 
electricity.  Attention  has  been  given  to  the  former  phase 
of  the  subject,  now  electromotive  force  must  be  considered. 

Electromotive  force  is  the  pressure  which  drives  an  electric 
current  through  a  conducting  medium;  other  terms  employed 
to  designate  this  concept  are  voltage  and  difference  of  po- 
tential. 

The  source  of  the  electromotive  force  in  an  electrical  cell 
is  to  be  sought  principally  at  the  points  of  contact  of  the 
electrodes  with  the  electrolytes  in  which  they  are  respec- 
tively immersed;  this  electromotive  force  is  practically  due 
to  chemical  action  between  the  metallic  electrodes  and  the 
chemical  solutions  in  which  these  are  placed. 

In  order  that  a  chemical  reaction  may  give  rise  to  electro- 
motive force,  the  substances  concerned  in  its  generation  must 
be  located  apart  from  one  another,  but  must  be  in  electrical 
connection  with  each  other  through  the  agency  of  a  metallic 
conductor  and  an  electrolyte.  Whenever  the  substances 
which  are  on  one  and  the  same  side  of  the  equation  sign  in  a 
true  chemical  reaction  are  placed  under  the  above  conditions, 
an  electrochemical  process  occurs. 

Consider  the  reaction : 

Zn  +  Cu  SO4  =  Zn  SO4  +  Cu. 


36  NOTES  ON  ELECTROCHEMISTRY. 

It  will  be  recalled  that  these  substances  form  an  electro- 
lytic cell  when  they  are  arranged  so  that  they  meet  the 
prescribed  conditions;  that  is  to  say,  when  the  zinc  is  away 
from  the  copper  sulphate  and  the  copper  is  removed  from 
the  zinc  sulphate,  but  when  both. are  in  electrical  connection 
by  the  intervention  of  an  electrolytic  medium  and  a  metallic 
wire.  The  system  here  referred  to  is,  in  fact,  the  well-known 
Daniell  cell. 

Conversely,  if  under  the  conditions  stated,  electrical  energy 
is  introduced  into  an  electrolyte,  chemical  changes  are  caused 
and  electrochemical  reactions  are  brought  about. 

To  effect  measurement  of  electromotive  force,  it  is  neces- 
sary to  establish  standards  for  comparison  and  to  have 
instruments  by  means  of  which  these  standards  may  be 
compared  with  the  electromotive  force  to  be  measured.  An 
accumulator  battery  supplies  a  reliable  and  uniform  source 
of  current;  a  direct  lighting  current  can  also  be  used  for 
this  purpose  by  causing  it  to  pass  through  proper  resist- 
ance and  by  using  a  part  of  the  current  for  the  work  in 
hand. 

It  is  customary  to  employ  either  Clark  cells  or  Weston 
Cadmium  cells  as  standards;  of  these  the  latter  are  preferable, 
because  they  are  scarcely  affected  at  all  by  changes  of  tem- 
perature. 

Instruments  used  to  record  voltage  are  either  direct- 
reading  voltmeters,  or  potentiometers.  As  it  is  desirable  to 
have  these  instruments  use  as  little  current  as  possible,  they 
are'  generally  constructed  with  high  resistances,  this  being 
insured  by  employing  numerous  windings  of  exceedingly  fine 
wire.  If  a  hot-wire  instrument  is  to  be  used  as  a  voltmeter, 
it  must,  of  course,  be  put  in  series  with  high  resistance. 

Voltmeters  are  not  as  desirable  as  potentiometers  because 
they  consume  some  current  and  require  occasional  recalibra- 
tion.  To  measure  electromotive  force  with  a  potentiometer, 
the  unknown  force  is  balanced  against  the  electromotive 


ELECTROCHEMISTRY.  37 

force  of  another  electric  current  of  known  value,  a  standard 
cell  being  used  in  substitution  for  the  unknown  electromotive 
force  to  be  measured.* 

Dissociation  Voltage. —  It  will  be  recalled  that  one  faraday, 
96,540  coulombs  of  electricity,  is  the  quantity  of  electricity 
which  will  separate  one  gram  equivalent  of  any  electrolyte; 
the  amount  of  electrical  potential  required  to  do  this,  how- 
ever, varies  with  the  heat  of  formation  of  the  electrolyte  to 
be  decomposed. 

The  amount  of  heat  set  free,  or  absorbed,  in  the  formation 
of  one  gram-molecule  of  a  substance  is  called  the  heat  of 
formation,  or,  the  heat  of  reaction  of  that  substance.  This 
value,  in  a  compound,  is  equal  to  the  difference  between  the 
heat  of  combustion  of  one  gram-molecule  of  the  compound 
and  the  heats  of  combustion  of  the  elements  which  form  it. 
It  represents  the  loss  of  chemical  energy  of  the  substances 
which  take  part  in  the  reaction. 

The  fact  that  the  amount  of  heat  necessary  to  decompose 
a  compound  into  its  constituents  is  precisely  the  same  as 
that  which  was  set  free  when  this  compound  was  formed, 
was  determined  by  Lavoisier  and  Laplace.  G.  H.  Hess,  in 
1840,  formulated  the  law  of  constant  heat  summation:  the 
heat  given  out  in  a  chemical  process  is  the  same  whether 
this  process  takes  place  in  one  or  in  several  stages.  This  is 
practically  an  individual  case  of  the  law  of  conservation  of 
energy,  for,  as  energy  can  be  neither  created  nor  destroyed, 
it  is  evident  that  the  amount  of  energy  required  for  the 
decomposition  of  a  compound  must  be  identical  with  the 
amount  of  energy  produced  when  that  compound  was  formed. 

The  heats  of  formation  of  chemical  compounds  are  given 
in  many  books  on  Physical  Chemistry,  and  of  course  in  all 
works  dealing  with  Thermochemistry. t 

*  Confer  :   Lehfeldt,  liber  ctt.,  p.  229. 

f  For  instance  in  Muir,  M.M.P.  and  Wilson,  D.M.:  "The  Elements  of 
Thermal  Chemistry,"  London,  1885. 


38  NOTES  ON  ELECTROCHEMISTRY. 

Possessed  of  such  thermal  data,  the  heats  of  formation, 
there  only  remains  to  be  learned  the  relation  between  the 
unit  of  heat  energy  and  the  unit  of  electrical  energy  in  order 
to  make  possible  a  calculation  of  the  electric  potential  re- 
quired to  effect  electrolytic  dissociation. 

The  unit  of  heat  energy  is  the  calorie,  the  amount  of  heat 
required  to  raise  the  temperature  of  1  gram  of  water  from 
15°  to  16°  C.,  hydrogen  scale.  The  unit  of  electrical  energy 
is  the  joule  —  the  product  obtained  by  multiplying  the 
coulombs  and  the  volts  of  an  electric  current.  One  joule 
will  raise  the  temperature  of  0.238882  gram  of  water  1°  C., 
hence,  in  round  numbers,  1  joule  =  0.24  caloric. 

Knowing  the  heat  of  formation  of  an  electrolyte,  it  is  only 
necessary  to  divide  this  number  by  0.24  to  ascertain  the 
joules  required  to  effect  the  electrolytic  decomposition  of 
the  compound,  and  the  joules  thus  found,  divided  by  96,540 
—  or  a  multiple  thereof  —  equal  the  number  of  volts  re- 
quired to  effect  the  desired  electrolysis. 

Lord  Kelvin  was  the  first  to  make  calculations  of  this  kind. 
It  is,  however,  important  to  remember  that  such  calcula- 
tions involve  acceptance  of  the  assumption  that  all  of  the 
chemical  energy  lost,  reappears  in  the  form  of  electrical 
energy.  This,  however,  is  by  no  means  always  the  case. 
In  some  reactions,  for  instance,  in  Clark's  cell  (Zn  :  Zn  SO4 
:  Hg2  SO4  :  Hg),  about  25  per  cent  of  the  chemical  energy 
lost  appears  as  heat.  In  other  instances,  however,  the 
agreement  between  the  calculated  values  and  the  values 
experimentally  determined,  is  very  close.  Thus,  for  the 
Daniell  cell  (Zn  :  Zn  SO4  :  Cu  SO4  :  Cu),  the  dissociation 
voltage  is,  calculated,  1.0872  volts;  experimentally  deter- 
mined, by  Jahn  at  0°  C.,  1.0962  volts. 

To  illustrate  the  calculation  of  dissociation  voltage  let 
us  consider  the  electrolytic  dissociation  of  potassium  chlo- 
ride. 

The  heat  of  formation  of    K  Cl  is  104,300  calories.     The 


ELECTROCHEMISTRY.  39 

amount  of  electrical  energy  equivalent  to  this  amount  of 
heat  energy  is,  therefore, 

104,300  -*-  0.24  =  434,584  joules, 

and  434,584+96,540        =  4.50 

hence,  4.50  volts  is  the  minimum  voltage  required  to  de- 
compose potassium  chloride  into  its  constituents,  potassium 
and  chlorine. 

One  faraday,  96,540  coulombs,  will  decompose  one  gram- 
molecular  weight  of  an  electrolyte  of  which  both  components 
are  monovalent.  Potassium  chloride  is  such  a  compound; 

the  atomic  weight  of  potassium  --=  39.15 

the  atomic  weight  of  chlorine  =  35.45 

hence,      the  molecular  weight  of  potassium  chloride  =  74 . 60 
Therefore,  it  will  require  434,584  joules,  or  96,540  coulombs 
at  a  potential  of  4.50  volts  to  decompose  74.60  grams  of 
potassium  chloride  into  its  constituents,  viz:  39.15  grams  of 
potassium  and  35.45  grams  of  chlorine. 

If  the  electrolyte  to  be  decomposed  has  a  divalent  con- 
stituent, 2  faradays  =  96,540  x  2  =  193,080  coulombs  will 
be  required  to  effect  the  desired  electrolysis,  and  it  is  this 
number  which  must  be  divided  into  the  joules  required,  to 
ascertain  the  minimum  dissociation  voltage.  This  minimum 
dissociation  voltage  may  also  be  readily  calculated  by  divid- 
ing the  heat  of  formation  of  the  compound,  expressed  in 
calories,  by  23,062  times  the  valence,  i.e.  the  number  of 
bonds.  This  factor,  23,062,  is  obtained  by  dividing  96,540 
•*•  4.18617,  for  one  calorie  is  equal  to  4.18617  joules. 

Thus,  in  the  case  of  potassium  chloride,  where  the  valence 
is  one,  and  the  heat  of  formation  is  104,300  calories: 

104,300  •+•  23,062  =  4.52  volts. 
In  the  case  of  magnesium  chloride,   Mg  C12,   where  there 


40  NOTES  OX  ELECTROCHEMISTRY. 

are  two  bonds  to  be  considered,  we  would  have  —  taking  the 
heat  of  formation  of  Mg  C12  as  217,300  calories: 

217,300  -*•  [23,062  X  2]  =  4.71  volts. 

The  dissociation  voltages  thus  found  are  valid  for  elec- 
trolytes in  aqueous  solution.  Fused  electrolytes  require 
somewhat  lower  voltages,  because  the  heat  of  fusion,  to  a 
certain  degree,  assists  the  reaction. 


CHAPTER   IV. 
ELECTROLYTIC   DISSOCIATION. 

Literature:  ABEGG,  R.,  and  HERZ,  W.  (English  translation  by  CALVERT, 
H.  T.):  "Practical  Chemistry."  London,  1901.  ARNDT,  K.: 
"  Grundbegriffe  der  allgemeinen  physikalischen  Chemie."  Berlin, 
1900.  GLASER,  F. :  "Indikatoren  der  Acidirnetrie  und  Alkali- 
metrie."  Wiesbaden,  1901.  HOPKINS,  N.  MONROE:  "Experimental 
Electrochemistry."  New  York,  1905.  KOHLRAUSCH,  F.,  and  HOL- 
BORN,  L.:  "Das  Leitvermogen  der  Elektrolyte."  Leipzig,  1898. 
LE  BLANC,  M. :  "Lehrbuch  der  Elektrochemie."  Leipzig,  1903. 
LEHFELDT,  R.  A.:  "Electrochemistry,"  Part  I,  General  Theory. 
New  York,  1904.  LOEB,  W. :  "Grundziige  der  Elektrochemie." 
Leipzig,  1897.  OSTWALD,  W. :  "Die  Wissenschaftlichen  Grundlagen 
der  Analytischen  Chemie."  Leipzig,  1901.  PERKIN,  F.  M. : 
"  Practical  Methods  of  Electrochemistry."  London,  1905. 

The  Ion  Theory.  —  The  Theory  of  Electrolytic  Dissociation, 
or  the  Ion  Theory,  as  it  is  frequently  termed,  was  formulated 
by  the  Swedish  scientist,  Svante  Arrhenius,  now  professor  in 
the  University  of  Stockholm,  after  he  had  become  acquainted 
with  the  brilliant  researches  of  J.  H.  Van't  Hoff;  these  were 
published  in  1887,  in  an  article  entitled,  "The  Role  of  Osmotic 
Pressure  in  the  Analogy  between  Solutions  and  Gases." 

By  the  term  osmotic  pressure  there  is  understood  the 
pressure  exerted  by  the  molecules  of  a  substance  in  solution 
when  such  solution  is  brought  into  contact  with  the  pure 
solvent,  or  when  such  a  solution  is  brought  into  contact  with 
another  solution  of  a  different  degree  of  concentration.  All 
substances  when  dissolved  in  water  exhibit  osmotic  pres- 
sure. 

The  true  cause  of  osmotic  pressure  is  as  yet  unknown,  but 
the  phenomena  of  osmotic  pressure  have  been  carefully 

41 


42  NOTES  ON  ELECTROCHEMISTRY. 

studied  and  some  very  important  relations  have  been  deter- 
mined. 

Van't  Hoff's  theory  of  osmotic  pressure  holds  that  the 
osmotic  pressure  of  a  substance  in  solution  is  the  same  as 
the  pressure  which  that  substance  would  exert  if  it  were  in 
the  gaseous  form  and  occupied  the  same  volume  at  the  same 
temperature.  In  other  words,  the  laws  of  gases  apply  also 
to  dilute  solutions;  the  laws  of  gas-pressure  are  valid  also 
for  the  osmotic  pressure  of  solutions. 

The  gas-equation  pv  =  RT  states  that  the  product  of 
the  volume  and  the  pressure  of  a  gas  is  directly  proportional 
to  the  absolute  temperature  and  to  the  value  R. 

7)    V 

R  is   a   constant  =  -^—^  •      In   the   equation  of  state  for 

~  4  O 

V  —  volume  in  cc.  of  a  gram-molecule  of  the  gas, 
p  =  pressure  in  grams  per  square  centimeter, 
T  =  absolute  temperature. 

The  molecular  weight  in  grams  (1  mol)  of  a  gas  at 
0°  C.  and  76  cm.  of  Hg  pressure,  has  a  volume  of  22.4 
liters;  in  the  space  of  1  liter  it  must,  therefore,  exercise  a 
pressure  of  22.4  atmospheres.  Now  it  follows,  according  to 
Van't  Hoff's  theory,  that  the  osmotic  pressure,  exercised 
by  a  solution  of  1  mol  of  a  substance  in  1  liter,  must  like- 
wise be  equal  to  22.4  atmospheres. 

A  solution  of  this  kind  (1  gram-molecular  weight  of  a 
solute  in  1  liter)  is  called  a  normal  solution. 

A  normal  solution  hence  exercises  an  osmotic  pressure 
of  22.4  atmospheres;  a  tenth-normal  solution  exercises  an 
osmotic  pressure  of  2.24  atmospheres,  and  so  on. 

It  is  evident,  then,  that  if  the  osmotic  pressure  of  a  solu- 
tion is  known,  that  the  molecular  weight  of  the  solute  can 
be  readily  determined. 

A  1  per  cent  solution  of  sucrose  gives  an  osmotic  pres- 
sure of  49.3  cm.  of  Hg. 


ELECTROLYTIC  DISSOCIATION.  43 

A  normal  solution  of  sucrose  would  give  a  pressure  equal 
to 

22.4    x  76  -  1702.4  cm.  Hg. 

The  1  per  cent  solution  contains  10  grams  of  sucrose  per 
liter,  hence 

10  :  x  :  :  49.3  :  1702.4,         x  =  345. 

This  is  in  close  agreement  with  the  molecular  weight  of 
sucrose  as  calculated: 

C  12  x  12  =  144 
H  22  x  1  =  22 
Oil  x  16  =  176 


342 

Many  solutions  which  wsre  examined  in  this  way  yielded 
returns  which  were  found  to  agree  with  this  theory  and 
which  bore  out  its  assumptions.  But  it  was  soon  ascer- 
tained that  all  the  salts,  acids,  and  bases  did  not  behave  in 
accordance  with  its  teachings. 

Solutions  of  these  substances  gave  osmotic  pressures 
greater  than  they  would  have  given  had  they  acted  in  con- 
formity with  the  laws  of  gases. 

It  was  furthermore  determined  that  those  substances 
which  in  aqueous  solutions  exert  an  osmotic  pressure  greater 
than  is  called  for  by  the  law  of  gas-pressure,  likewise  cause 
greater  lowerings  in  the  freezing-point  of  water,  produce 
greater  elevations  of  the  boiling-point,  and  effect  a  lower- 
ing in  the  vapor-tension  of  volatile  solvents:  last,  but  not 
least,  it  was  found  that  aqueous  solutions  of  these  substances, 
and  these  only,  could  conduct  the  electric  current. 

To  meet  the  exigencies  .of  the  case  it  was  proposed  to 
introduce  an  additional  factor  i  into  the  gas-equation,  thus 
making  the  latter  read : 

pv  =  iRT. 
This  factor  i  was  termed  the  Van't  Hoff  i,  from  its  originator. 


44  NOTES  ON   ELECTROCHEMISTRY. 

In  all  of  the  substances  named,  the  salts,  the  acids,  and 
the  bases,  the  value  of  i  is  always  greater  than  unity. 

Arrhenius,  reflecting  on  this  problem,  on  the  probable 
cause  of  these  numerous  discrepancies  between  Van't  Hoff's 
theory  of  osmotic  pressure  and  the  results  found,  recalled 
the  analogous  case  of  abnormal  vapor-pressures  exhibited  by 
iodine  and  by  some  other  substances  when  their  vapor- 
pressures  were  determined  at  high  temperatures. 

In  these  instances  the  explanation  had  at  last  been  reluc- 
tantly accepted,  that  a  dissociation  of  the  molecules  prob- 
ably occurred  at  high  temperatures. 

"  Therefore,"  wrote  Arrhenius,  "it  is  natural  to  assume 
that  substances  which  in  aqueous  solution  give  pressures 
that  are  too  great,  are  likewise  dissociated." 

Arrhenius  outlined  his  theory  in  a  letter  which  he  addressed 
in  the  early  part  of  1887  to  Oliver  Lodge,  secretary  of  the 
British  Association  Committee  for  Electrolysis.  Somewhat 
later  in  the  same  year  a  full  discussion  of  his  views  appeared 
in  the  Transactions  of  the  Swedish  Academy  of  Sciences,  in 
•which  journal  there  had  been  published,  in  1883,  another 
article  by  Arrhenius,  "  Galvanic  Conductivity  of  Very  Dilute 
Aqueous  Solutions-,"  in  which  he  may  be  said  to  have,  in 
a  measure,  foreshadowed  the  theory  of  electrolytic  dissocia- 
tion which  he  formulated  in  1887. 

The  essence  of  this  theory  of  Arrhenius  is,  of  course,  the 
deduction  that  the  osmotic  pressure  exercised  by  the  par- 
ticles into  which  molecules  may  become  dissociated  is  the 
same  as  the  osmotic  pressure  exercised  by  the  molecules 
themselves. 

In  other  words,  the  ion  theory  holds,  that  in  dilute  aqueous 
solutions  there  are  more  smallest  particles  of  the  dissolved 
'substance  (the  solute)  than  correspond  to  the  molecular 
weight  of  the  substance;  the  theory  accounts  for  this  by 
assuming  that  a  number  of  molecules  arc  dissociated,  elec- 
trolytically  dissociated,  in  such  solution. 


ELECTROLYTIC  DISSOCIATION.  45 

On  the  assumption  that  the  forces  holding  chemical  atoms 
together  in  molecules  are  of  electrical  origin,  J.  J.  Thomson 
explains  electrolytic  dissociation  of  molecules  into  ions  by 
ireans  of  electrical  induction. 

On  introducing  an  electrolyte,  sodium  chloride,  for  in- 
stance, into  a  dissociant  solvent,  say  water,  the  positive 
atom,  the  sodium,  will  induce  a  negative  charge  in  the  water, 
and  the  negative  atom,  the  chlorine,  will  induce  a  positive 
charge  in  the  water.  These  induced  electric  charges  almost 
neutralize  the  electric  charges  on  the  atoms  which  originally 
induced  them,  and  thus  the  attraction  between  the  atoms 
of  the  original  molecules  is  weakened  and  dissociation  ensues. 

The  amount  of  energy  possessed  by  two  electric  charges 
held  apart  by  any  medium  is  inversely  proportional  to  the 
specific  inductive  capacity  —  the  so-called  dielectric  con- 
stant of  that  medium. 

The  dielectric  constant  of  water  is  80.  Calvert  ascribes 
a  dielectric  constant  of  92.8  to  hydrogen  peroxide;  that  of 
hydrocyanic  acid  is  95.  In  consequence  of  the  high  specific 
inductive  capacity  of  water  electrolytic  dissociation  ensues 
readily  in  this  medium. 

The  actual  existence  of  free  ions  in  electrolytes,  the  fact 
that  they  bear  charges  of  electricity,  and  that  they  migrate 
under  the  influence  of  electric  force,  was  experimentally 
demonstrated  by  Ostwald  and  Nernst.  It  is  the  movement 
of  these  electric  charges  which  constitutes  an  electric  current 
within  an  electrolyte. 

As  previously  stated,  when  an  electric  current  passes 
through  a  conducting  solution,  part  of  the  ions  formed  in  the 
solution  move  towards  the  negative  electrode,  the  cathode. 
These  particles  are  termed  cathions;  they  bear  charges  of 
positive  electricity.  The  other  ions  move  towards  the  posi- 
tive electrode,  the  anode;  these  ions  are  termed  anions  and 
they  bear  charges  of  negative  electricity. 

These  terms  are  derived  from  the  Greek:  Ion  means  wan- 


46  NOTES  ON  ELECTROCHEMISTRY. 

derer;  cathion  means  descending,  because  the  cathions  in 
the  electrolyte  move  with  the  positive  current  towards  the 
cathode;  anion  means  ascending,  to  indicate  that  the  anions 
move  in  a  direction  opposite  to  that  taken  by  the  cathions. 
This  terminology  is  due  to  Faraday. 

Williamson,  in  1851,  and  again  Clausius,  in  1857,  assumed 
that  a  small  portion  of  ions  preexisted  in  solutions  and  that 
these  were  capable  of  conducting  the  electric  current;  these 
particles  were  designated  as  part-molecules. 

In  1887,  however,  it  was  generally  believed  that  the  elec- 
tric current  itself  induced  the  breaking  up  of  chemical  com- 
pounds into  the  particles  which  conveyed  the  electric  charge 
through  solutions  capable  of  conducting  electricity. 

It  was  Arrhenius  who  determined  that  the  number  of 
preexistent  ions  might  be  considerable,  and  that,  up  to  a 
certain  limit,  dilution  of  the  solution  increased  their  number. 

An  equivalent  amount  of  positive  and  of  negative  elec- 
tricity must  always  be  conveyed  by  the  ions,  for  no  free 
electricity  can  be  detected  in  solutions  of  electrolytes,  hence 
for  every  cathion  which  separates  at  the  cathode,  an  anion 
must  give  up  a  corresponding  electric  charge  at  the  anode. 

Ions  possess  definite  electric  valencies,  and  for  every  dyad 
ion  which  separates  at  one  electrode,  another  dyad  ion  or 
two  monovalent  ions  must  separate  at  the  other  electrode. 
Among  the  more  important  monovalent  cathions  are: 

H  (in  the  acids),  K,  Na,  Ag.    .    .    . 
Among  the  divalent  cathions: 

Ca,  Ba,  Mg,  Fe  (in  ferro-compounds),    . 
Among  the  trivalent  cathions : 

Al,  Bi,  Sb,  Fe  (in  ferri-compounds),    .    .    . 
Among  the  monovalent  anions: 

OH  (in  the  bases),     Cl,     Br,     I,     N08,     C1O3  .    .    . 


ELECTROLYTIC*  DISSOCIATION. 
Among  the  divalent  anions: 


4T 


S,     SO4,     MnO4   ..... 

The  following  table  of  the  chemical  elements  in  their 
electrochemical  sequence,  is  given  by  N.  Monroe  Hopkins. 
Each  element  is  electropositive  to  every  element  whose 
name  is  placed  before  its  own,  and  is  electronegative  to  all 
elements  whose  names  follow  its  own : 


Oxygen 
Sulphur 
Nitrogen 


Selenium 

Phosphorus 

Arsenic 

Chromium 

Vanadium 

Molybdenum 

Tungsten 

Boron 

Carbon 

Antimony 

Tellurium 

Tantalum 

Columbium 

Titanium 

Silicon 

Tin 

Hydrogen 

Gold 

Osmium 

Iridium 


Negative  Atoms. 

Fluorine 
Chlorine 

Positive  Atoms. 

Platinum 

Rhodium 

Ruthenium 

Palladium 

Mercury 

Silver 

Copper 

Uranium 

Bismuth 

Gallium 

Indium 

Germanium 

Lead 

Cadmium 

Thallium 

Cobalt 

Nickel 

Iron 

Zinc 

Manganese 


Bromine 
Iodine 


Lanthanum 

Didymium 

Cerium 

Thorium 

Zirconium 

Aluminium 

Scandium 

Erbium 

Ytterbium 

Beryllium 

Magnesium 

Calcium 

Strontium 

Barium 

Lithium 

Sodium 

Potassium 

Rubidium 

Caesium 


It  must,  however,  not  be  forgotten  that  the  terms  posi- 
tive and  negative  in  electricity  are  merely  relative  —  it  all 
depends  on  the  conditions  in  which  the  substances  are  placed. 


4&  XOTES  ON  ELECTROCHEMISTRY. 

If  two  metals  are  placed  in  a  solution  which  attacks  the 
one  metal  and  does  not  attack  the  other,  the  metal  which 
goes  into  solution  is  electropositive  to  the  other  metal;  the 
metal  which  goes  into  solution  forms  the  negative  pole  in 
the  outside  circuit. 

Zinc  is  attacked  by  dilute  nitric  acid  and  by  dilute  sul- 
phuric acid,  and  even  in  solutions  of  ammonium  chloride 
and  potassium  hydrate  it  will  go  into  solution  replacing 
other  metals;  zinc,  therefore,  is  electropositive  to  them  all. 

It  has  been  previously  explained  that  all  ions  of  the  same 
valency  bear  identical  electric  charges,  although  the  masses 
of  the  atoms  with  which  these  charges  are  associated  are  not 
equal.  Ions,  in  short,  may  be  regarded  as  combinations  of  ma- 
terial atoms  with  electric  atoms,  with  the  so-called  electrons. 

Ions  of  different  substances  vary  considerably  in  their 
electro-affinity,  that  is,  in  the  degree  of  power  with  which 
they  hold  their  electric  charges.  Those  ions  which  hold 
their  electric  charges  firmly  are  termed  strong,  those  which 
readily  part  with  their  charges  are  called  weak  ions.  As 
a  rule,  strong  ions  are  given  to  the  forming  of  soluble  com- 
pounds, compounds  which  dissociate  readily  when  brought 
into  solution.  Weak  ions,  on  the  other  hand,  are  generally 
given  to  the  forming  of  compounds  which  are  less  soluble, 
that  is,  to  the  forming  of  compounds  which  ionize  only  to 
a  slight  degree  when  placed  into  contact  with  a  solvent. 

If  an  ion  of  a  low  degree  of  electro-affinity  encounters  a 
non-ionized  substance  which  possessess  a  greater  degree  of 
electro-affinity  when  in  the  ionic  state  than  it  itself  possesses, 
then  the  electric  charge  will  be  transferred  from  the  former 
to  the  latter. 

For  instance,  if  metallic  zinc  is  brought  into  contact  with 
lead  in  the  ionic  condition  the  lead  suffers  precipitation  as 
metallic  lead,  while  the  zinc  goes  into  solution,  zinc  ions  being 
formed.  Lead  precipitates  copper;  copper,  in  turn,  precipi- 
tates mercury,  and  so  on. 


ELECTROLYTIC    DISSOCIATION.  49 

When  an  electric  current  is  passed  through  an  electrolyte 
the  ions  move  through  the  solution  to  the  electrodes  and 
there  give  up  their  charges  of  electricity,  provided  that  the 
tension  of  the  electrodes  is  sufficient  to  overcome  the  electro- 
affinity  of  the  ions  for  their  electric  charges.  When  this 
happens  the  atoms  separate  in  their  elemental  condition,  un- 
less they  take  part  in  some  secondary  reactions  in  which 
they  enter  into  new  chemical  relations. 

The  capacity  of  forming  ions  does  not  depend  alone  on 
the  substance  which  goes  into  solution,  the  solvent  plays 
an  important  role  in  this  transaction.  This  property  is 
referred  to  as  the  dissociative  power  of  the  solvent.  Water, 
as  previously  mentioned,  has  a  high  dissociant  power;  formic 
acid,  methyl  and  ethyl  alcohol  are  fairly  strong  dissociants. 
Chloroform,  benzol,  and  many  other  organic  substances  lack 
this  dissociant  power  entirely;  these  substances  are,  there- 
fore, not  electrolytes,  that  is,  they  do  not  conduct  an  electric 
current  between  electrodes  immersed  in  them. 

Gram- molecular  equivalent  solutions  of  most  neutral  salts 
are  practically  completely  ionized  in  1000  liters  of  water. 
As  a  rule,  salts  containing  monovalent  ions  are  ionized  to  a 
greater  extent  than  salts  of  multivalent  ions. 

The  strong  acids,  among  which  must  be  counted  hydrochloric, 
hydroiodic,  hydrobromic,  nitric,  and  sulphuric  acids,  are  under 
like  conditions  all  ionized  to  about  the  same  degree  as  the 
salts.  Phosphoric  and  sulphurous  acids  are  usually  ionized 
to  the  extent  of  only  10  per  cent;  silicic  acid  and  boracic 
acid  are  hardly  ionized  at  all. 

Walker  and  Cormack  have  determined  the  degree  of  ioniza- 
tion  of  the  following  substances  in  one-tenth  normal  solutions: 

Hydrochloric  acid .    ....    .    .    .  91.4% 

Acetic  acid 1.3% 

Carbonic  acid     .........     0.174% 

Sulphuretted  hydrogen 0.075% 

Boracic  acid 0.013% 


50  NOTES  ON  ELECTROCHEMISTRY. 

Among  the  strong  bases  are  the  hydroxides  of  the  alkalies 
and  the  hydroxides  of  the  alkaline  earthy  metals.  Ammonia 
and  magnesia  are  bases  of  a  lower  degree  of  ionization,  and 
the  hydroxides  of  the  di-  and  tri-valent  metals  and  most 
of  the  alkaloids  must  be  counted  among  the  weak  bases. 

The  ion  theory  has  proven  of  special  value  in  the  secur- 
ing of  a  clearer  understanding  of  the  problems  of  analytical 
chemistry,  and  it  is  to  Wilhelm  Ostwald  that  science  is 
chiefly  indebted  for  signal  achievements  in  this  direction. 

The  study  of  many,  if  not  of  most  chemical  reactions,  may 
be  regarded  .as  a  study  of  the  behavior  of  ions,  for  ions  have 
and  preserve  certain  individual  characteristic  properties, 
which  they  exhibit  without  regard  to  the  presence  or  absence 
of  other  ions  and  molecules.  The  properties  of  aqueous 
solutions  of  most  salts  are  but  the  sum  of  the  properties  of 
their  constituent  ions. 

That  this  point  of  view  materially  simplifies  analytical 
chemistry  is  evident  when  one  considers  that  instead  of  hav- 
ing to  study  and  to  remember  the  reactions  of,  say,  one 
hundred  different  compound  substances,  all  that  it  is  neces- 
sary to  know  are  the  reactions  of  ten  cathions  and  ten  anions 
which  enter  into  the  composition  of  the  above-named  one 
hundred  compounds. 

The  terms  salt,  acid,  and  base,  have  here  been  repeatedly 
used,  and  it  will  be  necessary  to  give  their  definitions  as 
understood  in  the  light  of  the  ion  theory.  Salts  are  com- 
pounds which,  when  they  are  dissolved,  break  up,  wholly 
or  in  part,  into  cathions  and  anions.  Acids  are  salts  in 
which  the  cathions  are  always  hydrogen  ions;  bases  are  salts 
in  which  the  anions  are  ^lw;ays  hydroxyl  ions. 

Strong  acids  are  those  which^ -contain  numerous  hydrogen 
cathions  in  unit  volume  —  for  the  characteristic  properties 
of  acids  depend  on  their  hydrogen  ions. 

Strong  bases  are  those  which  contain  many  hydroxyl 
anions  in  unit  volume,  for  it  is  upon  the  presence  of  the 


ELECTROLYTIC   DISSOCIATION.  51 

hydroxyl    ions   that   the    characteristic    properties    of    bases 
depend. 

Acidity  and  basicity  of  solutions  hence  rest  solely  upon, 
and  vary  with,  respectively,  the  amount  of  hydrogen  and 
of  hydroxyl  ions  present. 

The  hydrogen  ions  of  acids  behave  differently  from  hydro- 
gen occurring  in  other  combinations;  the  hydroxyl  ions  of 
bases  likewise  react  differently  from  the  hydroxyl  groups 
occurring  in  other  compounds.  Thus,  the  hydrogen  ions 
of  acids  will  redden  litmus;  the  hydroxyl  ions  of  bases  will 
turn  red  litmus  blue.  Water  and  hydrogen  peroxide  both 
contain  hydrogen  and  hydroxyl,  yet  neither  shows  the  above- 
mentioned  reactions  with  litmus.  Water  and  hydrogen 
peroxide  are,  therefore,  at  once  recognized  as  not  belonging 
to  either  the  acids  or  bases. 

Pure  water  is  ionized  only  to  a  very  slight  degree,  less 
than  one  mol,  that  is  to  say,  less  than  18  grams  in  10,000,000 
liters  —  14  grams  is  the  figure  that  approximates  more 
closely  to  the  real  value.  To  express  it  differently,  in  one 
million  liters  of  water  there  are  0.078  grams  of  hydrogen 
ions  and  1.326  grams  of  hydroxyl  ions.  These  values  are 
the  values  for  the  temperature  of  18°  C.  The  number  of 
ions  in  a  given  solution  increases  very  rapidly  with  the 
temperature,  approximately  at  the  rate  of  8  per  cent  per 
degree.  As  water  is  so  slightly  dissociated,  it  is  but 
natural  that  hydrogen  ions  and  hydroxyl  ions  when  they 
meet  in  a  solution  should  immediately  combine  to  form 
non-dissociated  water. 

From  the  viewpoint  of  the  ion  theory  the  neutralization 
of  an  acid  in  an  aqueous  solution  is  looked  upon,  not  as  the 
union  of  an  acid  with  a  base  radical,  but  as  the  union  of 
the  hydrogen  ions  of  the  acid  with  the  hydroxyl  ions  of  the 
base;  the  process  of  neutralization  in  an  aqueous  solution 
hence  consists  essentially  in  the  formation  of  water. 

The  heat  of  neutralization,  for  instance,  of  the  reaction: 
HC1  +  NaOH  =  Na  +  Cl  +  H2O, 


52  NOTES  ON  ELECTROCHEMISTRY. 

is  due  to  the  heat  of  chemical  combination  of  the  hydrogen 
ions  with  the  hydro xyl  ions,  the  sodium  cathions  aixd  the 
chlorine  anions  remaining  unchanged  in  the  solution. 

Bearing  in  mind  that  an  ion  consists  of  the  atom  of  an 
element  plus  one,  two,  three,  or  more  electric  charges  ac- 
cording to  its  valence  —  a  fraction  of  the  unit  charge  is  never 
carried  —  ions  can,  in  writing,  be  readily  differentiated  from 
the  atoms  of  elements  by  adding  to  the  chemical  symbols 
for  the  latter  some  conventional  sign  to  indicate  the  char- 
acter of  the  electric  charge  the  ions  bear,  and  to  specify  the 
number  of  these  charges. 

A  small  circle  or  period  has  been  selected  to  represent  a 
charge  of  positive  electricity,  a  dash  or  a  comma,  to  typify 
a  negative  charge;  the  number  of  these  symbols  indicate 
the  number  of  electric  charges  borne  by  an  ion.  Thus,  an 
ion  of  hydrogen  is  represented  by  the  symbol  H*,  an  ion  of 
calcium  by  the  symbol  Ca'V  The  anion  chlorine,  is  Cl'; 
oxygen  O";  the  complex  anion  hydroxyl,  OH'. 

The  term  ion,  introduced  by  Faraday,  was  by  him  em- 
ployed in  connection  with  the  stems  of  the  chemical  names 
of  substances  to  indicate  the  substances  from  which  the  ions 
originated.  A  systematic  nomenclature  of  the  ions  has, 
however,  as  yet,  not  been  adopted,  although  James  Walker* 
has  proposed  a  system  of  naming,  as  he  expressed  it,  "  the 
material  of  the  ions  as  distinguished  from  the  particles  them- 
selves." Cathions  he  would  indicate  by  adding  the  termi- 
nation ion  to  the  stem  of  the  word,  and,  when  necessary, 
would  disclose  the  electrical  valency  of  the  ion  by  prefixing 
a  Greek  numeral.  Thus  he  suggested: 

Hydrion  .............  H' 

Sodion Na* 

Calcion Ca" 

Diferrion     . Fe" 

Triferrion    .    .    ...    .    .    .  '.    .    .    .  Fe"% 

*  Chemical  News,  1901,  Vol.  84,  p.  162. 


ELECTROLYTIC   DISSOCIATION.  53 

The  names  of  the  an  ions  he  proposed  forming  in  such  a 
manner  as  to  indicate  the  kind  of  salt  from  which  the  anions 
are  derived.  For  instance,  anions  formed  from  -ate  salts 
would  have  the  termination  -anion ;  those  formed  from  -He 
salts,  the  ending  -osion  —  to  recall  the  -ous  acids  which  give 
rise  to  -He  salts.  Anions  from  -ide  salts  would  receive  the 
termination  -idion.  For  Instance: 

Hydroxidion     ...,,;..,.   OH' 

Sulphidion ,    .    .   S" 

Sulphosion .    .   SOs" 

Sulphanion :-..-•    SO/' 

The  term  ionogen  has  been  suggested  by  Alexander  Smith  * 
to  indicate  any  and  all  substances  which  can  suffer  ionization. 

When  a  solid  goes  into  solution  it  exercises  pressure,  the 
so-called  solution-pressure,  and  this  corresponds  to  the  osmo- 
tic pressure  of  a  saturated  solution.  If  the  molecules  of  a 
solid  are  not  dissociated  in  the  process,  the  action  ceases 
when  a  certain  pressure  has  been  attained;  if  the  substance 
is  an  ionogen,  the  action  continues  until  the  ions  and  the 
non-dissociated  molecules  respectively  have  attained  to  a 
definite  concentration. 

This  relation  can  be  expressed  by  a  formula  which  holds 
true  in  many,  but  not  in  all,  instances: 

Km  =  ca. 
In  this  formula: 

K  —  the  constant  of  ionization, 

m  =  the  concentration  of  the  non-dissociated  molecules, 

c  =  the  concentration  of  the  cathion, 

a  =  the  concentration  of  the  anion. 

The  unit  of  concentration  is  one  mol  per  liter.  In  other 
words,  the  formula  Km  =  ca,  where  it  is  valid,  states  that 

*  Chemical  News,  1901,  Vol.  84,  p.  279. 


54  NOTES  ON   ELECTROCHEMISTRY. 

the  product  of  the  ions  present  in  a  solution  bears  a  fixed 
relation  to  the  amount  of  non-dissociated  molecules  in  that 
solution. 

This  formula  is  an  interesting  one.  Nernst  determined 
that  the  concentration  of  the  non-dissociated  molecules  does 
not  change  in  a  saturated  solution;  in  a  case  where  both  m 
and  K  are  unchanging  the  product  ca  must  also  have  a 
constant  value.  This  product  is  termed  the  solubility  pro- 
duct. It  represents  the  number  of  grams  per  liter  to  which 
the  concentration-product  of  the  ions  can  attain  and  yet 
have  the  ions  exist  as  ions  in  the  solution. 

Should  one  add  to  a  saturated  solution  wherein  such  an 
equilibrium  obtains,  any  other  solution  which  has  an  ion 
in  common  with  an  ion  of  the  solution  first  named,  then  the 
equilibrium  would  be  disturbed  and  the  solubility-product 
having  been  exceeded,  the  respective  values  would  suffer 
readjustment.  This  indicates  the  condition  which  must 
be  established  in  order  to  secure  a  practically  complete 
precipitation  of  any  given  substance,  an  excess  of  the  pre- 
cipitating reagent  must  be  employed.  The  same  principle 
applies  to  the  washing  of  precipitates;  in  order  to  avoid  the 
solvent  action  of  the  washing-fluid  care  must  be  taken  to 
have  the  washing-fluid  contain  ions  identical  with  some  of 
those  instrumental  in  forming  the  precipitate. 

The  ions  of  most  of  the  lighter-weight  metals,  and  those 
of  the  halogens,  are  colorless;  those  of  the  heavier  metals 
are  colored;  for  instance,  cobalt  ions  are  red,  nickel  ions 
and  di-ferric  ions  are  green.  The  use  of  indicators  in  aci- 
dimetry  and  alkalimetry  is  based  on  the  fact  that  in  the  in- 
dicators used  the  color  of  the  non-dissociated  molecule  is 
different  from  the  color  of  the  ion  or  ions  formed  therefrom. 
The  ion  theory  affords  a  plausible  explanation  of  the  phe- 
nomena involved  and  it  will  be  of  interest  to  consider  a  case 
in  illustration;  phenolphthalein,  which  is  much  used  as  an 
'indicator,  will  answer  the  purpose. 


ELECTROLYTIC    DISSOCIATION.  55 

The  formula  of  phenolphthalein  is  C20HI4O4.  Its  configu- 
ration is  probably 

/C6H4OH 
C-C6H4OH 
\C6H4 

O-CO 

Phenolphthalein  is  a  weak  acid,  that  is  to  say,  it  ionizes  in 
water  only  to  a  slight  degree.  Its  non-dissociated  molecule 
is  colorless,  its  cathion  H*  is  colorless,  its  complex  anion  is 
red.  This  anion  shall  here  be  denoted  by  the  symbol  P.P'. 

If  KOH  is  added  to  a  colorless  (alcoholic)  solution  of 
phenolphthalein  there  will  be  present  in  the  solution: 

Ions  from  phenolphthalein:  H*  cathions  and  P.P'.  anions; 

From  the  KOH  solution:  K*  cathions  and  (OH)'  anions. 

The  H'  cathions  of  the  phenolphthalein  will  combine  with 
the  (OH)'  anions  of  the  potassium  hydrate  and  form  non- 
dissociated  water-molecules.  Abstraction  of  the  H'  cathions 
will,  however,  induce  other  molecules  of  phenolphthalein  to 
dissociate  in  order  to  restore  the  equilibrium  indicated  by 
the  formula  Km  =  ca. 

These  reactions  continuing,  there  will  ultimately  be  present 
in  the  solution  an  accumulation  of  K*  cathions  and  of  com- 
plex phenolphthalein  anions.  The  latter,  as  previously 
stated,  are  red  and  hence  —  so  says  the  ion  theory  —  the 
red  color  of  the  solution. 

By  means  of  the  reactions  indicated,  the  potassium-salt 
of  phenolphthalein  has  been  formed.  As  a  rule  the  potas- 
sium salts  of  weak  acids  are  ionized  to  a  greater  degree  than 
the  acids  from  which  they  are  formed.  In  consequence, 
the  solution  contains  toward  the  end  of  the  reaction  a 
greater  number  of  phenolphthalein  anions,  and  these  impart 
the  red  color  to  the  solution. 

If  a  strong  acid,  hydrochloric  acid,  for  instance,  be  added 
to  a  solution  of  this  description,  then  there  would  be  present 
in  the  solution: 


56  NOTES  ON  ELECTROCHEMISTRY. 

Ions  from  the  potassium-salt  of  phenol phthalein:  K* 
cathions  and  P.  P/  anions. 

Ions  from  the  hydrochloric  acid :  H*  cathions  and  Cl'  anions. 

The  H*  cathions  would  come  into  contact  with  the  phe- 
nolphthalein  anions,  and  as  the  ionization  constant  of  phe- 
nolphthale.'n,  a  weak  acid,  is  smaller  than  that  of  its  potassium 
salt,  the  H*  cathions  and  the  phenolphthaleiii  anions  would 
recombine  to  form  non-dissociated  phenolphthaleiii.  These 
molecules  are  colorless  and  in  consequence  the  solution 
would  lose  its  red  color  which,  it  will  be  remembered,  was 
caused  by  the  phenolphthalein  anions.  The  solution  would 
again  turn  colorless. 

Litmus  is  an  acid  indicator;  azolithmin  is  its  active  color- 
ing principle.  The  non-dissociated  molecules  are  red,  the 
anions  are  blue.  Addition  of  a  base  to  litmus  results  in 
the  formation  of  water  and  of  a  more  highly  ionized  salt, 
and  the  blue  color  of  the  anions  imparts  a  blue  color  to  the 
solution.  Addition  of  a  strong  acid  to  such  a  solution  will 
cause  some  of  the  original  non-dissociated  red  molecules  of 
litmus  to  reform,  and,  in  consequence,  a  red  color  will  again 
appear. 

If  titrations  are  attempted  in  very  dilute  aqueous  solu- 
tions, then  the  H'  cathions  and  the  (OH)'  anions  of  the  water 
will  take  an  active  part  in  the  reaction.  This  phenomenon 
is  referred  to  as  hydrolytic  dissociation,  or  hydrolysis. 

Hydrolysis  is  apt  to  prove  a  serious  cause  of  disturbance 
when  weak  acids  or  weak  bases  are  titrated.  In  the  case 
of  strong  acids  and  strong  bases,  that  is  to  say,  with  those 
that  are  ionized  to  a  considerable  extent,  hydrolysis  is  a 
matter  of  but  little  moment. 

An  example  of  hydrolytic'  dissociation  is  afforded  by  the 
sodium  salt  of  phenol.  On  ionization  this  yields  Na"  cath- 
ions and  phenol  C6H6O'  anions.  The  latter  enter  into  chem- 
ical union  with  the  H*  cathions  of  the  water  used  as  sol  vent - 
and,  as  a  result,  phenol,  C6H^OH,  is  formed.  This  can  be 


ELECTROLYTIC    DISSOCIATION.  57 

distinctly  recognized  by  its  odor.  The  (OH)'  anions  formed 
by  the  ionization  of  the  water  impart  an  alkaline  reaction 
to  the  solution. 

'  An  aqueous  solution  of  cyanide  of  potassium  affords  an- 
other illustration  of  hydrolytic  action.  In  consequence  of 
such  action  the  solution  always  contains  an  appreciable 
quantity  of  HCy.  The  reaction  of  the  solution  is  alkaline; 
this  is  owing  to  the  presence  of  hydro xyl  anions. 

Application  of  the  principles  of  the  ion  theory  to  problems 
of  physiological  chemistry  has  also  led  to  some  very  inter- 
esting results,  but  a  consideration  of  these  here  would  take 
us  too  far  afield. 

The  principal  lines  of  evidence  to  be  adduced  in  support 
of  the  theory  of  electrolytic  dissociation,  are  in  brief  resume, 
the  following : 

a.  The  parallelism  of  behavior  of  electrolytes  and  gases  — 
osmotic  pressure  phenomena. 

.b.  The  abnormal  lowering  of  the  freezing-point  of  solu- 
tions by  electrolytes.  Where  all  normal  solutions  of  non- 
electrolytes,  i.e.,  solutions  containing  one  gram-molecule 
of  solute  in  one  liter  of  solvent,  lower  the  freezing-point  of 
pure  water  1.86°  C.,  all  electrolytes  depress  the  freezing-point 
of  pure  water  to  a  much  greater  degree,  possibly  again  as 
much. 

c.  The  abnormal  elevation  of  the  boiling-point  of  water 
by.  electrolytes.     Normal   solutions  of   non-electrolytes  raise 
the  boiling-point  of  water  by  a  given  amount,  identical  for 
all  non-electrolytes;  electrolytes   in  normal  solutions  effect 
this  to  a  much  higher  degree. 

d.  The   thermal-neutralization   phenomena   of    acids   and 
bases.     The  neutralization  of  a  normal  solution  of  an  acid 
by  a  base,  or  vice  versa,  liberates  an  amount  of  heat  that  is 
constant,   13,700    calories.     This  value    represents   the    heat 
of  formation  of  water,  and  only  this.     In  all  neutralization 
experiments  of  the  kind  referred  to,  water  is  an  invariable 


58  NOTES  ON  ELECTROCHEMISTRY. 

product.  If  molecules  were  formed  of  the  other  constituents, 
besides  the  molecules  of  water  produced  by  the  chemical 
combination  of  the  hydrogen  and  hydroxyl,  their  respective 
heats  of  formation  would  be  manifest  in  the  reaction.  This, 
however,  does  not  occur,  and  hence  the  inference  is  drawn 
that  these  constituents  exist  in  the  solution  as  ions,  and  not 
as  molecules. 

To  cite  an  illustration: 

NaOH  +  HC1  =  Nad  +  H2O 

The  heat  of  this  reaction  is  13,700  calories,  the  molecular 
heat  of  formation  of  water. 

The  heat  of  formation  of  Nad  is  9760  calories,  and  yet 
this  heat  value  does  not  appear.  Why  not?  The  reason  is, 
because  the  compound  Nad  is  not  formed  in  the  reaction, 
the  components  of  this  compound  remaining  in  the  solu- 
tion as  ions,  as  ions  of  sodium  and  of  chlorine. 

e.  The  fact  that  chemical  reactions  will  not  take  place 
between  perfectly  dry  electrolytes;  a  dissociant  is  required 
to  loosen  the  affinity  between  the  atoms  of  the  molecules 
and  thus  set  free  the  ions  which  are  assumed  to  be  the  re- 
acting units  of  all  chemical  changes. 

A  great  many  data  may  be  offered  in  support  of  the  theory 
of  electrolytic  dissociation.  However,  it  must  not  be  over- 
looked that  a  number  of  facts,  experimentally  obtained, 
have  as  yet  not  been  brought  into  harmony  with  its  teach- 
ings. 

Louis  Kahlenberg*  cites  among  other  objections  to  this 
theory,  that  the  color  of  solutions  is  independent  of  their 
ability  to  conduct  electric  currents,  whereas  the  ion  theory 
holds  that  the  color  of  aqueous  solutions,  at  least,  is  due 
to  their  ions;  he  denies  that  free  ions  are  the  immediate 

*  Journal  Phys.  Chem.,  1901,  Vol.  5,  p.  339;  Trans.  Faraday  8oc.t 
1905,  Vol.  1,  p.  42. 


ELECTROLYTIC  DISSOCIATION.  59 

agents  concerned  in  chemical  reactions,  for  the  reason  that 
such  reactions  occur  also  in  solutions  that  are  insulators, 
for  instance,  in  benzene. 

Again,  the  theory  does  not,  as  yet,  accord  sufficient  weight 
to  the  part  which  solvents  play  in  the  formation  of  solutions. 
The  interesting  relations  which  rest  on  the  interdependence 
of  solute  and  solvent  still  call  for  much  further  research  and 
explanation.  Furthermore,  numerous  thermochemical  data 
appear  to  be  at  variance  with  the  values  the  theory  would 
seem  to  call  for;  its  teachings  are  not  always  valid  even  for 
fairly  dilute  solutions.  Reychler  actually  asserts  the  theory 
of  electrolytic  dissociation  to  be  in  opposition  to  many 
thermochemical  data  secured  by  experiment. 

Notwithstanding  these  shortcomings,  there  can  at  least 
be  no  doubt  or  question  as  to  the  great  value  of  the  ion 
theory  in  the  harmonization  and  correlation  of  numerous 
data,  and  of  the  stimulus  which  it  has  given  to  scientific 
thought  and  inquiry.  Considering  its  bearing  on  the  elec- 
tron theory,  it  is  an  interesting  fact  that  the  electric  charges 
transported  by  ions  in  electrolytes  are  identical  with  the 
charges  conveyed  by  the  particles  in  gases  when  electric 
discharges  are  passed  through  gases. 

Conductivity.  —  By  conductivity  in  general,  there  is 
meant  the  property  of  conducting  a  current  of  electricity. 
In  an  electrolyte,  it  is  the  joint  effect  of  convection  of  the 
cathions  and  anions;  it  is  an  additive  property;  and  the 
conductivity  of  an  electrolyte  represents  the  amount  of 
electricity  which  is  conveyed  in  unit  time  by  unit  electro- 
motive force. 

Conductivity  is  the  reciprocal  of  resistance;  the  greater 
the  latter,  the  smaller  the  conductivity.  Conductivity  is 
usually  expressed  in  terms  of  a  unit  styled  the  mho  cubic- 
centimeter  unit;  the  term  mho  is  simply  the  word  ohm  re- 
versed in  order  to  indicate  that  the  unit  of  conductivity  is 
the  reciprocal  of  the  unit  of  resistance.  This  unit  ohm 


60  XOTES  OX  ELECTROCHEMISTRY. 

expresses  the  conductivity  of  a  substance  one  centimeter- 
cube  of  which  has  a  conductance  of  one  mho  between  two 
parallel  sides.  In  other  words,  if  a  current  density  is  stated 
in  amperes  per  square  centimeter  and  the  potential  gradient 
in  volts  per  centimeter,  the  conductivity  will  be  expressed  in 
mhos  per  centimeter  cube. 

It  has  been  experimentally  demonstrated  that  the  trans- 
mission of  electric  impulses  through  electrolytes  is  practi- 
cally instantaneous.  This  can  only  be  accounted  for  by  the 
assumption  of  the  presence  of  free  ions  about  the  electrodes 
which  give  up  their  charges  the  instant  an  electric  current 
is  sent  through  the  electrolyte. 

From  the  interesting  researches  of  N.  Monroe  Hopkins  *' 
it  appears  that  "  electrolytes  of  equal  resistance  conduct 
the  electric  current  with  a  definite  velocity,  regardless  of 
the  composition  of  the  electrolytes  or  the  length  of  the  con- 
taining vessel."  This  investigator  also  determined,  that  an 
electrolyte  conducts  the  electric  current  just  as  fast  as  a 
metallic  conductor,  provided,  that  an  equal  ohmic  resist- 
ance, of  a  non-inductive  type,  is  furnished. 

Molecular  conductivity  is  the  appellation  given  to  the 
conductivity  of  solutions  which  contain  one  gram-molecule 
of  the  electrolyte;  it  increases  with  the  temperature  and 
with  the  degree  of  dilution.  As  first  pointed  out  by  Kohl- 
rausch  the  molecular  conductivity  of  an  electrolyte  is  equal 
to  the  sum  of  the  velocities  of  migration  of  the  ions. 

Let,       m  =  molecular  conductivity, 

a  ••=  velocity  of  migration  of  the  anion, 
c  —  velocity  of  migration  of  the  cathion, 
x  =  fraction  of  electrolyte  dissociated   into    ions,, 
then,          m  =  x  (a  +  c). 

On  attaining  to  infinite  dilution  the  dissociation  of  an 
electrolyte  into  its  ions  becomes  complete,  an.1,  in  that  case, 

x  =  1,     and     woo  =  a  +  c. 
*  Scient.  Am.  Suppl    1905,  p.  24305. 


ELECTROLYTIC   DISSOCIATION.  61 

Prom  these  equations  it  follows  that, 

m 


x  = 


m  oc 


which  expresses  the  fact  that  the  degree  of  dissociation  at 
.any  dilution  is  equal  to  the  ratio  of  the  molecular  conduc- 
tivity at  that  state  to  the  molecular  conductivity  at  infinite 
dilution. 

Equivalent  conductivity  is  the  conductivity  of  equivalent 
quantities;  it  is  the  quotient  obtained  by  dividing  the  con- 
centration into  the  conductivity. 

Let          K  =  conductivity, 

t]  —  concentration  in  grain-equivalents  per  cubic 

centimeter, 

v  =  volume  in  cubic  centimeters  per  gram-equiv- 
alent, i.e.,  the  dilution, 
A  =  equivalent  conductivity, 
jp" 

then,  A  =  —  . 

f 

or,  A  =   Kv. 

The  equivalent  conductivity  of  an  electrolyte,  base  or 
acid,  increases  with  dilution,  but  for  infinitely  great  dilu- 
tion approaches  a  finite  limit.  Direct  measurement  of  the 
equivalent  conductivity  of  an  electrolyte  can  be  made  by 
placing  a  one  gram-equivalent  solution  between  two  elec- 
trodes set  one  centimeter  apart,  these  electrodes  serving  as 
two  walls  of  the  vessel  containing  the  electrolyte. 

The  direct  determination  of  conductivity  of  an  electrolyte 
by  passing  an  electric  current  through  an  electrolyte  of  uni- 
form cross-section  and  measuring  the  current  strength  and 
the  voltage  direct  between  the  electrodes,  is  not  always 
feasible,  as  in  many  instances  the  electrodes  become  polar- 
ized. In  such  cases  the  measurement  is  effected  by  aid  of 


62  NOTES  ON  ELECTROCHEMISTRY. 

an  alternating  current  which  precludes  the  polarization  of 
the  electrodes,  each  of  the  electrodes  serving  alternately 
as  anode  and  as  cathode. 

The  method  of  Kohlrausch,  a  modified  Wheatstone  bridge 
arrangement,  is  frequently  used  in  determining  the  resist- 
ance of  an  electrolyte.  An  alternating  current  from  the 
secondary  of  a  small  induction  coil  is  employed  for  the 
reason  given,  and  a  telephone  receiver  is  used  in  place  of  a 
galvanometer.  When  the  Wheatstone  bridge  is  not  in 
balance  a  humming  noise  is  heard  in  the  telephone;  in 
making  the  measurement  the  bridge  resistance  must  be 
adjusted  in  such  a  way  as  to  secure  silence,  or,  at  least,  a 
minimum  of  sound.  Electrodynamo meters  may  also  be 
used  in  place  of  the  telephone  arrangement.  As  the  con- 
ductivity of  an  electrolyte  is  greatly  affected  by  changes 
in  temperature,  the  vessel  in  which  the  measurements  are 
made  should  be  placed  in  a  thermostat. 

Pure  solids  at  ordinary  temperatures  have  but  a  low 
conductivity.  It  is  therefore  of  interest  to  know  that  some 
substances,  notably  the  salts,  exhibit  a  high  conductivity 
when  fused;  this  conductivity  increases  with  a  rising  tem- 
perature. 

The  specific  conductivity  of  fused  nitrate  of  silver  at 
310°  C.  is,  for  instance,  expressed  in  reciprocal  ohms,  equal 
to  1.09;  at  375°  C.  it  is  1.32.  The  specific  conductivity  of 
nitrate  of  silver  in  solution,  dissociated  into  ions  to  the 
extent  of  about  75  per  cent,  is  only  0.11  reciprocal  ohms  at  a 
temperature  of  25°  C.;  the  conductivity  of  the  fused  salt 
therefore  far  exceeds  that  of  the  salt  in  solution. 

Thus  far  it  has  been  found  impossible  to  determine  the 
degree  of  dissociation  of  a  fused  salt  into  ions,  and  their 
conductivity  values  can  therefore  only  be  determined  at 
given  temperatures.  R.  Lorenz*  has,  however,  demonstrated 
that  the  laws  of  Faraday  are  valid  also  tor  fused  salts. 

*  Ziltschr.  fur  Elektrochemie,  1900,  p.  277  ;   1901,  p.  753. 


ELECTROLYTIC    DISSOCIATION.  63 

The  fact  that  certain  metallic  oxides  when  at  very  high 
temperatures,  though  not  hi  a  state  of  fusion,  will  conduct 
electricity  has  been  taken  advantage  of  by  Nernst  in  the 
making  of  his  incandescent  lamps,  the  filaments  of  which 
consist  of  oxide  of  magnesium;  the  same  property  has  also 
been  made  use  of  in  the  construction  of  the  tantalum  lamps 
manufactured  by  Siemens  &  Halske. 

Migration  of  Ions.  —  An  electric  field  is  a  space  wherein 
electrical  influences  are  exerted.  An  ion  moving  in  a  field 
which  is  uniform  is  acted  on  by  a  constant  force,  but  the 
speed  with  which  it  moves  is  not  a  uniformly  accelerated 
speed,  as  might  be  supposed,  because  the  resistance  of  the 
liquid  through  which  the  ion  moves  causes  its  velocity  to 
be  materially  retarded.  The  intensity  of  the  electric  field 
in  which  an  ion  moves  determines  its  velocity;  this  is  called 
the  potential  gradient,  and  is  expressed  in  volts  per  centi- 
meter. 

The  velocity  of  an  ion  under  a  gradient  of  one  volt  per 
centimeter  is  termed  its  mobility,  and  this  is,  as  shown  by 
Bredig  and  Ostwald,  a  periodic  function  of  the  atomic  weight 
of  the  elements.  Hence  the  mobilities  of  the  different  ions 
differ,  and  the  determination  of  these  values  is  a  matter  of 
importance. 

The  relative  mobility  of  anions  and  cathions  was  deter- 
mined by  Hittorf  in  the  following  manner:  Two  porous 
plates  were  inserted  in  a  trough  dividing  the  trough  into 
three  compartments.  These  compartments  were  all  filled 
with  an  electrolyte,  for  instance,  with  a  solution  of  sulphate 
of  copper;  a  copper  anode  and  a  copper  cathode,  respectively, 
were  inserted  in  the  end  compartments,  and  an  electric  cur- 
rent was  passed  through  the  solution. 

After  the  current  had  been  passed  through  the  electrolyte 
for  a  short  time,  samples  were  taken  from  each  of  the  three 
compartments  and  analyzed.  The  sample  removed  from 
the  cathode  chamber  was  found  to  be  less  concentrated,  the 


64  NOTES  ON  ELECTROCHEMISTRY. 

sample  from  the  anode  chamber  was  found  to  be  more  con- 
centrated than  before  the  current  wad  passed,  while  the 
sample  from  the  middle  chamber  was  found  to  have  retained 
its  original  concentration. 

Taking  the  whole  current  conveyed  as  unity,  and  x  as  that 
part  of  the  current  conveyed  by  the  anion,  then  1  —  x  of 
course  represents  the  fraction  of  the  current  transported 
by  the  cathion.  One  faraday  requires  one  gram-equivalent 
of  ions  for  its  transport,  in  consequence  there  must  pass 
across  any  section  in  the  interior  of  the  liquid  x  equiva- 
lents of  anions  in  the  direction  opposite  to  the  direction 
taken  by  the  current,  and  1  —  x  equivalents  of  cathions  in 
the  direction  of  the  current.  This  x  is  known  as  Hittorfs 
number,  the  migration  ratio  of  the  anion. 

Electric  currents  produced  by  the  movement  of  the  ions 
are  proportional  to  their  mobilities: 

cathionic      anionic       , 

:  ,   : : 1  —  x :  x 

current         current 

The  loss  in  concentration  of  the  solution  in  the  cathode 
compartment  is  equal  to  the  gain  in  concentration  of  the 
solution  in  the  anode  compartment.  If,  for  instance,  in 
the  case  just  discussed,  0.2  faraday  had  passed  and  the 
change,  in  each  chamber,  had  been  found  to  be  0.124  equiva- 
lents, the  migration  ratio  of  the  anion  would  be: 

0.124  -5-  0.2  =  0.620 

Values  differing  slightly  from  this  have  been  found  by  dif- 
ferent experimenters,  but  the  true  value  undoubtedly  closely 
approximates  to  the  figure  given. 

Hittorf,  the  pioneer  in  this  line  of  work,  carried  out  a 
great  number  of  determinations  on  migration  ratios;  the 
form  of  apparatus  for  the  study  of  individual  cases  being, 
of  course,  suitably  modified  to  meet  the  requirements  of 
the  occasion.  A  convenient  model  for  the  demonstration 


ELECTROLYTIC  DISSOCIATION.  65 

of  Hittorf's  theory  of  the    migration  velocities  of  ions,  has 
been  described  by  Getman.* 

Several  methods  have  been  devised  for  measuring  the 
absolute  velocities  of  ions,  among  others  by  Whetham  and 
Lodge.  The  latter  measured  the  absolute  velocity  of  hydro- 
gen ions  in  the  following  manner.  Into  a  hot  aqueous  solu- 
tion of  gelatine,  which  he  prepared,  he  incorporated  some 
sodium  chloride  as  an  electrolyte  and  colored  the  whole 
mass  red  by  the  addition  of  a  little  alkaline  solution  of  phe- 
nolphthalein.  This  gelatine  preparation,  while  hot,  he  poured 
into  a  straight  glass  tube,  both  ends  of  which  were  bent  at 
right  angles.  Each  end  of  the  glass  tube  dipped  into  a 
beaker  containing  dilute  sulphuric  acid;  in  one  of  these 
beakers  a  platinum  anode  was  placed,  in  the  other,  a  plati- 
num cathode,  and  a  voltmeter  was  joined  across  these  elec- 
trodes to  indicate  the  potential  gradient  of  the  current. 

As  soon  as  an  electric  current  was  sent  through  the  system, 
hydrogen  ions  proceeded  to  pass  from  the  anode  through 
the  gelatine  preparation  in  the  glass  tube  to  the  cathode 
in  the  other  beaker.  The  hydrogen  ions  displaced  the 
sodium  from  the  sodium  chloride,  and,  combining  with  the 
chlorine,  formed  hydrochloric  acid.  This  acid,  of  course,  at 
once  decolorized  the  phenolphthalein,  and  thus  the  progress  of 
the  reaction  could  be  closely  traced  and  accurately  measured. 

Through  careful  experiments  of  this  kind  Lodge  ascer- 
tained the  velocity  of  a  hydrogen  ion  to  be  1.1580  centi- 
meters per  minute,  or  less  than  three-quarters  of  a  meter 
per  hour,  a  low  speed  at  best,  and  yet  the  hydrogen  ions 
exceed  all  others  in  speed  of  migration. 

The  absolute  velocity  of  some  one  ion  having  been  accu- 
rately determined,  the  absolute  velocities  of  other  ions  can 
be  easily  deduced  from  their  relative  velocities,  values  which, 
it  will  be  remembered,  can  be  readily  determined  by  Hittorf's 
method. 

*  Science,  1905,  Vol.  21,  p.  153. 


CHAPTER   V. 
ELECTRO-ANALYSIS. 

Literature:  CLASSEN,  A.  (English  translation  by  HERRICK,  W.  H.): 
"Quantitative  Chemical  Analysis  by  Electrolysis."  New  York, 
1887.  ELBS,  K.:  "Die  Akkumulatoren.  Leipzig,  1896.  HOPKINS, 
N.  M.:  "Experimental  Electrochemistry."  New  York,  1905. 
FOERSTER,  F.:  "  Elektrochemie  wiisseriger  Losungen."  Leipzig, 
1905.  LOEB,  W.:  "Die  Elektrochemie  der  organischen  Verbin- 
dungen."  HALLE,  A.  S.  1905.  LORENZ,  R.:  "  Elektrochemisches 
Praktikum."  Gottingen,  1901.  NISSENSON,  H.:  "Einrichtungen 
von  Elektrolytischen  Laboratorien."  HALLE,  A.  S.  1903.  PETERS, 
F.:  "Angewandte  Elektrochemie,"  Vol.  I.  Wien,  1897.  SMITH, 
E.  F.:  "Electrochemical  Analysis."  Philadelphia,  1902. 

Electro-Analysis.  —  Various  conceptions  have  been  and  are 
entertained  of  the  nature  of  the  electrolytic  process,  but  in 
view  of  the  most  recent  developments  it  may,  perhaps,  be 
best  to  look  upon  the  phenomena  occurring  in  the  electro- 
lysis of  solutions  as  actions  and  reactions  in  which  ions 
play  the  leading  role. 

It  will  be  recalled  that  ions  are  denned  as  compounds 
of  atoms  and  electrons.  Under  the  influence  of  the  electric 
current  the  ions  move  towards  the  electrodes,  of  course  the 
anions  seeking  the  anode  and  the  cathions  seeking  the  cath- 
ode. When  the  ions  have  come  within  acting  distance  of 
the  electrode  towards  which  they  are  traveling,  a  discharge, 
that  is  to  say,  a  neutralization  of  the  electric  charges  which 
they  bear,  takes  place.  This  division  of  ions  into  electrons 
and  into  atoms,  which  were  held  in  combination  with  these 
electrons,  liberates  the  atoms  in  a  condition  in  which  their 
chemical  affinity  can  come  most  strongly  into  play.  This 
condition  is  frequently  designated  as  the  nascent  state,  the 


ELECTRO- A  NA  L  YSIS.  6  7 

"  status  nascendi";  if  the  ions  which  have  thus  suffered 
discharge  are  compound  ions,  the  materialistic  nuclei  which 
remain  are  unsaturated  compounds,  and  as  such  also  display 
strong  chemical  affinity. 

If  there  is  no  other  substance  present  in  an  electrolytic 
solution  with  which  the  atoms  or  unsaturated  nuclei  can 
enter  into  chemical  combination,  these  atoms  or  nuclei 
assume  the  molecular  state.  Thus,  for  instance,  in  the 
electrolytic  decomposition  of  water,  if  the  hydrogen  and 
oxygen  set  free  find  no  other  substance  present  with  which 
they  can  enter  into  chemical  combination,  then  these  ele- 
ments are  liberated  as  hydrogen  and  as  oxygen  gas  respec- 
tively. 

The  electric  discharge  of  ions  takes  place  in  accordance 
with  Faraday's  laws.  If  the  conditions  are  such  that  sev- 
eral reactions  may  occur,  the  speed  with  which  iors  are 
discharged  is  a  very  important  factor,  for,  if  the  speed  of  re- 
action of  the  discharged  ions  with  the  depolarizer  is  greater 
than  the  speed  of  discharge  of  the  ions  then  there  will  be  no 
liberation  of  the  discharged  ions  in  the  molecular  state; 
this  can  frequently  be  observed  in  processes  of  oxidation 
and  reduction. 

As  electrochemical  reactions  are  confined  to  the  imme- 
diate neighborhood  of  the  electrodes,  the  rate  at  which  such 
reactions  proceed  is  dependent  upon  the  concentration  of  the 
ions.  But  the  concentration  of  the  ions  is  determined  by 
the  current  strength,  the  size  of  the  electrode  surface,  and 
the  concentration  of  the  depolarizer,  and  these  items  must 
therefore  be  very  carefully  considered  and  adjusted  in  every 
electrolytic-  operation  to  ensure  the  desired  result. 

The  chief  characteristic  of  an  electrolytic  process,  as  com- 
pared with  a  purely  chemical  process,  is  the  consumption  of 
energy  in  the  former  in  lieu  of  the  consumption  of  material 
in  the  latter;  mother  words,  an  electric  current  effects  changes, 
for  instance,  oxidations  and  reductions,  which  in  chemical 


68  NOTES  OX  ELECTROCHEMISTRY. 

processes  are  induced  only  by  the  intervention  of  chemicals. 
If  a  chemical  change  is  brought  about  directly  by  the 
action  of  electrical  energy,  if  the  electric  current  is  allowed  to 
act  upon  an  electrolyte,  the  action  is  spoken  of  as  a  direct 
action ;  if  the  electric  energy  must  first  suffer  transformation 
into  some  other  form  of  energy,  for  instance,  into  heat  or 
light,  the  process  is  spoken  of  as  an  indirect  action.  The 
manner  in  which  the  electric  action  known  as  the  silent  dis- 
charge is  effected  is  as  yet  but  little  understood,  although 
unquestionably  many  electrochemical  effects  in  nature  arc 
brought  about  by  this  agency. 

In  effecting  the  electrolysis  of  organic  substances  two  cases 
must  be  distinguished:  the  body  acted  upon  may  be  an 
electrolyte,  or  it  may  be  a  non-electrolyte. 

In  the  latter  case  the  ions  which  are  to  transport  the 
electric  charges  must  be  furnished  from  some  other  source^ 
through  addition  of  some  electrolyte.  The  ions  thus  intro- 
duced will,  under  the  influence  of  the  electric  current,  travel 
towards  the  electrodes,  and  the  organic  substance  is  acted 
upon  by  these  ions  only  at  the  moment  of  their  discharge. 
A  substance  thus  entering  into  chemical  combination  with 
the  atomic  constituent  of  an  ion  at  the  moment  of  its  dis- 
charge is  termed  a  depolarizer. 

Two  classes  of  depolarizers  may  be  distinguished,  anodic 
and  cathodic  depolarizers. 

Cathodic  Depolarizers.  —  The  process  taking  place  at  the 
cathode  is  termed  reduction;  the  principal  cathions,  that  is, 
the  ions  liberated  at  the  cathode,  are  ions  of  the  metals  and 
of  hydrogen;  a  few  organic  cathions  are  also  known.  Sub- 
stances which  can  either  take  up  hydrogen  or  give  gut  oxygen, 
or  do  both,  are  known  as  reducible  substances;  in  other 
words,  they  are  oxidizing  agents,  and  their  special  function 
is  the  neutralization  of  positive  charges. 

Anodic  Depolarizers.  —  Anodic  depolarizers  are  agents 
which  destroy  negative  charges.  If  oxygen  be  added,  or 


ELEC  TRO-A  NAL  Y  SIS.  6  9 

if -hydrogen  be  abstracted,  or  if  both  of  these  phenomena 
.proceed  simultaneously,  the  process  is  designated  as  a  process 
Of  oxidation. 

Thus,  a  substance  submitted  to : 

REDUCTION,  OXIDATION, 

Gains  hydrogen,  Loses  hydrogen, 

Loses  oxygen,  or  both.  Gains  oxygen,  or  both. 

Reversible  Reactions  and  Cells.  —  A  process  at  a  given 
electrode  is  reversible  when  the  substances  formed  in  this 
process  are  the  same,  whether  the  electric  current  flows 
from  this  electrode  or  towards  it. 

Thus,  in  the  Daniell  cell: 

Zn  :  ZnSO4     :  CuSO4     :  Cu 
solution     solution 

if  the  electric  current  flows  from  the  zinc  into  the  electrolyte 
zinc  ions  will  go  into  solution;  if  the  current  is  sent  in  the 
reverse  direction,  zinc  ions  will  travel  towards  the  zinc  elec- 
trode and  zinc  will  be  deposited  on  that  electrode. 

Electrodes  reversible  with  respect  to  cathions  are  termed 
electrodes  of  the  first  order;  these  generally  consist  of  a 
metal  placed  in  a  solution  of  some  one  of  its  own  salts.  Elec- 
trodes reversible  with  respect  to  anions  are  termed  electrodes 
of  the  second  order;  these  can  be  made  by  placing  some 
insoluble  compound  containing  the  anion  required  on  some 
metal  and  then  placing  the  electrode  thus  prepared  into  a 
solution  of  the  same  anion. 

Reversible  cells  may  consist  of  any  combination  of  elec- 
trodes. A  reversible  cell  may  be  defined  as  a  cell  which 
can  be  restored  to  its  original  condition  by  an  expenditure 
of  electrical  energy  equal  to  the  maximum  electrical  energy 
obtainable  from  it  at  constant  temperature.  An  irrever- 
sible cell  is  one  in  which  the  original  condition  cannot  be 
restored  by  reversing  the  direction  of  the  current  flow;  for 


70  NOTES  OA'  ELECTROCHEMISTRY. 

instance,  the  original  voltaic  pile,  made  of  zinc,  sulphuric 
acid,  and  silver,  is  of  this  type.  The  water  voltameter  is 
another  illustration  of  an  irreversible  cell.  Cells  of  this  kind, 
as  a  rule,  furnish  a  rather  high  electromotive  force  at  the 
start;  this,  however,  depreciates  as  the  action  proceeds,  for 
the  electrodes  suffer  polarization.  Reversible  cells,  on  the 
other  hand,  yield  a  current  almost  constant  in  electromotive 
force  as  long  as  they  continue  in  action,  for  in  these  the 
electrodes  do  not  suffer  polarization. 

If  the  electromotive  force  of  a  cell  is  determined,  the 
voltage  represents  the  difference  of  potential  between  the 
electrodes.  Whenever  there  is  a  contact  of  dissimilar  sub- 
stances electromotive  force  appears,  but  it  is  only  the 
electromotive  force  caused  by  the  contact  between  the 
metal  electrodes  and  the  electrolyte  in  which  they  re- 
spectively are  immersed,  that  here  calls  for  comment.  To 
this  value  the  term  electrode-potential  is  given ;  it  represents 
the  work  expended  in  conveying  the  unit  quantity  of  elec- 
tricity between  electrode  and  electrolyte. 

An  explanation  of  this  action  was  first  suggested  by  Nernst,* 
who  showed  that  the  process  might  be  conceived  of  as  an 
osmotic  process  by  ascribing  to  each  metal  the  property  of 
forcing  electrically  charged  particles,  ions,  into  a  liquid  with 
which  the  metal  is  in  contact.  This  forcing  of  the  ions  into 
the  liquid  takes  place  with  a  pressure  peculiar  to  each  metal 
and  is  invariable  at  constant  temperature.  The  metal  may  thus 
be  regarded  as  a  sort  of  reservoir  of  ions  wherein  these  ions 
are  stored  under  a  greater  or  less  pressure,  and  this  pressure 
is  designated  as  the  electrolytic  solution  pressure  of  the  metal. 

Whenever  electrical  energy  is  developed,  both  positive 
and  negative  electricity  come  simultaneously  into  existence. 
In  the  metallic  electrodes  as  such,  the  particles  are  without 
electric  charges;  at  the  instant,  however,  that  a  particle 

*Zeit8chriff,  Phys.  C'hemie.  1889,  Vol.  4,  p.  129. 


ELECTRO-ANALYSIS.  71 

passes  from  an  electrode  into  an  electrolytic  solution  the 
particle  assumes  a  positive  charge  and  thus  becomes  an  ion; 
at  the  same  instance  the  metallic  electrode  acquires  a  nega- 
tive charge  of  equal  intensity.  Each  additional  ion  which 
enters  into  the  solution  increases  the  positive  charge  of  the 
solution  while  the  electrode  becomes  correspondingly  more 
and  more  charged  with  negative  electricity. 

Electric  charges  of  opposite  sign  attract  one  another  and 
one  can  thus  conceive  of  a  layer  of  positively  charged  ions 
held  in  attraction  by  a  negatively  charged  electrode,  a  differ- 
ence in  potential  being  thus  established.  The  electrostatic 
attraction  of  this  layer  opposes  the  tendency  of  the  electro- 
lytic solution  pressure  of  the  electrode  to  force  more  ions 
into  the  solution ,  and  when  these  counterforces  are  in  equi- 
librium the  action  comes  to  a  halt.  As  the  electric  charges 
carried  by  the  ions  are  very  great,  such  equilibrium  is  estab- 
lished even  when  but  a  few  ions  have  passed  from  the  elec- 
trode into  the  solution. 

If  a  metallic  electrode  be  immersed  in  a  solution  of  one 
of  its  own  salts,  the  metallic  ions  therein  will  —  by  osmotic 
pressure  —  oppose  the  admission  of  more  ions  of  their  own 
kind.  If  this  osmotic  pressure  of  the  ions  in  the  solution 
is  exactly  in  equilibrium  with  the  solution  pressure  of  the 
electrode,  no  ions  will  be  projected  from  the  latter  into  the 
solution,  and  the  electrode  will  therefore  not  be  charged 
with  negative  electricity. 

On  the  other  hand,  if  the  osmotic  pressure  is  greater  than 
the  electrolytic  solution  pressure,  the  metallic  ions  are  driven 
from  the  solution  on  to  the  electrode  and  the  electrode  is 
thereby  charged  with  positive  electricity.  The  solution- 
losing  some  of  its  positively  charged  ions  while  its  content 
of  negatively  charged  anions  is  not  decreased,  becomes  nega- 
tively charged;  the  electrostatic  difference  is  thus  continu- 
ously increased  until  it  counterbalances  the  osmotic  pressure, 
and  then  equilibrium  is  restored. 


72  NOTES  ON  ELECTROCHEMISTRY. 

The  electromotive  force  of  a  cell  can  be  calculated  from 
the  osmotic  pressure  of  the  solutions  about  the  electrodes, 
for,  if  a  substance  is  allowed  to  pass  isothermally  from  one 
condition  into  another  it  is  immaterial  how  such  a  trans- 
formation occurs,  whether  osmotically  or  electrically. 

Knowing  the  maximum  amount  of  external  work  which  a 
process  can  accomplish  in  an  isothermal  transformation,  the 
problem  is  a  simple  one,  for  the  work  which  can  be  done  by 
ions  in  passing  from  a  given  osmotic  pressure  to  another 
can  be  transformed  without  loss  into  electrical  energy. 

The  fundamental  formula  by  which  the  electromotive 
force  of  an  element  is  calculated  from  the  osmotic  pressure 
of  the  solutions  about  the  electrodes,  is: 


In  this  formula 

P  —  potential, 
r  =  valence  of  the  ions, 
E0  =  quantity  of  electricity, 

RTln—  =  amount  of  energy  transformed  into  work  in  a  gas 
which  expands  isothermally  from  a  pressure  p1 
to  a  pressure  p2. 

This  last  formula  also  holds  for  a  solution  which  passes 
isothermally  from  one  osmotic  pressure  to  another. 

In  a  Dauiell  cell  the  difference  in  potential  between  the 
two  electrodes  is  practically  1.1  volts.  Of  this,  0.5  volt  is 
the  potential  difference  between  the  zinc  electrode  and  the 
zinc  sulphate  solution  —  the  electrolyte  in  which  it  is  im- 
mersed, and  the  balance,  0.6  volt,  is  the  potential  difference 
between  the  copper  electrode  and  the  solution  of  copper 
sulphate  in  which  this  electrode  is:  immersed. 


ELECTRO-ANALYSIS.  73 

The  term  electro-affinity  is  used  to  designate  the  electrode 
potential  in  solutions  which  contain  1  gram-equivalent  per 
liter  of  the  ion  given  off  by  the  electrode;  solutions  of  this 
concentration  are  called  normal  solutions.  An  electrode  is 
either  positive  or  negative  to  a  normal  solution  of  its  ions, 
and  its  electro-affinity  is,  by  the  majority  of  writers,  denoted 
accordingly  as  positive  or  negative.  The  electromotive 
force  of  a  cell  whose  electrodes  are  reversible  with  respect 
to  any  ion,  is  the  algebraic  difference  between  the  electro- 
affinities  of  the  two  ions. 

In  normal  solutions  the  electrode-potential  increases  for 
cathions  and  decreases  for  anions  with  the  concentration 
of  the  electrolyte.  In  other  words,  the  electrode  potential 
is  determined  by  the  concentration  of  that  part  of  the  elec- 
trolyte in  actual  contact  with  the  electrode.  It  is  therefore 
important  that  the  electrolyte  be  kept  in  motion  by  a  stirrer, 
or,  that  the  electrode  be  kept  revolving  in  the  solution,  for 
by  these  means  the  concentration  of  a  solution  is  kept  fairly 
uniform  and  an  even  deposition  of  the  metal  precipitated 
by  the  electric  current  is  secured.  If  some  precaution  be 
not  taken  to  secure  a  uniform  concentration  of  the  solution, 
the  concentration  of  the  electrolyte  about  the  cathode  will 
decrease  and,  in  consequence,  the  electrode-potential  of 
the  cathode  will  be  lowered,  while  the  concentration  of  the 
electrolyte  at  the  anode  will  be  increased,  and  the  electrode- 
potential  of  the  anode  will  be  raised  in  consequence.  When 
this  occurs,  a  fall  of  potential  results,  indicative  of  the  work 
done  in  bringing  about  these  differences  in  concentration. 
This  phenomenon  is  known  as  concentration  polarization; 
it  occurs  whenever  any  perceptible  amount  of  chemical 
action  is  taking  place. 

The  dissociation  voltages  previously  discussed  are,  of  course, 
to  be  considered  only  as  minimum  voltages  based  upon  the 
assumption  that  the  electrolytic  process  takes  place  slowly 
and  with  weak  currents.  Heavier  currents  invariably  cause 


74  NOTES  ON  ELECTROCHEMISTRY. 

concentration  polarization,  and  to  overcome  this  higher  volt- 
ages are  required. 

The  electrode-potential  of  an  ion  depends  upon  its  chemical 
nature  and  upon  the  amount  in  which  this  ion  is  present  in 
an  electrolyte.  If,  therefore,  more  than  one  kind  of  cathion 
is  present  in  an  electrolyte,  that  cathion  will  be  first  dis- 
charged which  has  the  greater  electrode-potential.  Through 
such  discharge,  however,  its  concentration  will  be  decreased 
and  thereby  its  electrode-potential  will  be  lowered;  when 
the  electrode-potential  of  both  cathions  is  identical,  both 
will  be  discharged  simultaneously. 

If  there  are  two  anions  present  in  an  electrolyte,  that 
anion  having  the  lower  potential  will  be  the  first  to  be  dis- 
charged; through  this  its  concentration  will  be  reduced  and 
its  electrode-potential  will  be  raised.  When  both  anions 
have  attained  to  the  same  electrode-potential  they  will  suffer 
simultaneous  discharge. 

These  facts  explain  why  the  current  density  —  the  quo- 
tient obtained  by  dividing  the  current  strength  by  the  elec- 
trode surface,  and  generally  expressed  in  terms  of  amperes 
per  100  square  centimeters  of  electrode  surface  —  plays  so 
important  a  part  in  electrolysis. 

Entirely  distinct  from  concentration  polarization  is  the 
phenomenon  termed  chemical  polarization.  This  is  due  to 
some  new  chemical  substance  or  substances  formed  by  the 
electric  current  and  the  consequent  substitution  of  new 
electrode  surfaces  for  those  electrode  surfaces  with  which 
the  electrolytic  operation  was  begun.  Thus,  in  the  elec- 
trolysis of  water  the  gases  liberated  by  the  action  of  the 
electric  current,  hydrogen  and  oxygen,  have  a  great  tendency 
to  polarize  the  electrode  surfaces  chemically. 

Such  a  polarization  produces  a  back-pressure,  a  reverse 
electromotive  force,  which,  at  times,  diminishes  the  effective 
electromotive  force  very  materially. 

The    amount    of    such    back-pressure    can    be    practically 


ELECTRO-ANALYSIS.  75 

measured  by  first  reading  the  voltage  across  the  two  elec- 
trodes as  usual,  then  turning  off  the  current  and  noting  the 
position  at  which  the  indicator  in  the  voltmeter  halts  for 
a  brief  space  of  time  ere  it  travels  on  to  zero.  That  point 
where  it  halts  marks  the  polarization  voltage. 

If,  for  instance,  the  full  working  voltage  in  an  experi- 
ment be  5  volts,  the  halting-point  be  at  3  volts,  and  the 
amperage  3.5,  then  the  resistance  of  the  cell,  i.e.,  the  reverse 
electromotive  force  of  the  cell  is  : 


A  means  of  overcoming  chemical  polarization  is  the  plac- 
ing of  the  anode  in  a  solution  of  a  salt  of  the  metal  of  which 
the  anode  is  made,  or  the  use  of  an  oxidizing  agent,  a  so- 
called  depolarizer,  which  oxidizes  the  product  of  electrolysis 
that  would  otherwise  polarize  the  electrode. 

Sources  of  Current.  —  In  choosing  a  source  for  current 
supply  for  analytical  purposes,  the  great  consideration  is 
the  securing  of  a  current  which  shall  have  sufficient  strength 
(amperage)  and  which  shall  possess  a  potential  (voltage) 
as  constant  as  possible. 

Use  can  be  made  of  primary  batteries  (cells),  of  thermo- 
piles, dynamos,  accumulators,  and  of  a  direct  lighting  cur- 
rent. 

Generally  speaking,  electrical  elements,  or  cells,  are  devices 
for  carrying  on  electrochemical  reactions.  Cells  which  yield 
an  electrical  current  are  called  voltaic  cells.  These  can  be 
made  to  serve  as  sources  of  supply,  but  are  open  to  several 
objections.  Some  yield  too  weak  a  current,  having  an 
internal  resistance  which  is  too  high;  others  polarize  too 
rapidly,  and  this,  of  course,  causes  a-  rapid  falling  off  in  cur- 
rent; others  again  emit  noxious  fumes  and  vapors. 

If  cells   are    to    be   used  possibly  the  best  is  the  Edison 


76  NOTES  OX   ELECTROCHEMISTRY. 

Primary  battery,  or  the  Daniell  cell.     The  latter  consists  of 

Zn:  ZnSO4:Cu:CuSO4 
The  Bunsen  cell  is  made  of — 

-      Zn:ZnSO4:C:HNO3. 

In  this  cell,  the  carbon,  gas-carbon,  or  graphite,  dips  into 
nitric  acid  which  is  contained  in  a  cup  or  cylinder  of  porous 
earthenware  or  clay.  The  zinc  is  generally  well  amalgamated 
to  avoid  local  currents  which  are  very  destructive  to  the 
electrode.  The  chromic  a,cid  cell  is  a  modification  of  the 
Bunsen  cell;  it  contains  potassium  dichromate  as  a  depola- 
rizer—  the  positive  pole  is  carbon,  the  negative  pole  is 
zinc,  well  amalgamated. 

Cells  can  be  grouped  for  a  high  electromotive  force  or 
for  an  increased  quantity  of  current. 

To  obtain  a  high  electromotive  force  the  cells  should  be 
linked  in  series,  that  is,  the  positive  pole  of  one  cell  should 
be  linked  to  the  negative  pole  of  another  cell;  zincs,  for  in- 
stance, to  carbons.  The  total  electromotive  force  of  a  set 
of  cells  thus  linked  in  series  is  equal  to  the  voltage  of  an 
individual  cell  multiplied  by  the  number  of  cells  so  linked. 
By  thus  linking  in  series,  the  internal  resistance  of  the  system 
is,  of  course,  also  increased. 

To  increase  the  quantity  of  electric  current  cells  must  be 
linked  in  parallel,  that  is,  all  the  positive  poles  are  joined 
together,  and  all  the  negative  poles  are  joined  together. 
This  arrangement  decreases  the  internal  resistance;  the  total 
internal  resistance  of  a  system  linked  in  parallel  is  equal  to 
the  resistance  of  an  individual  cell  divided  by  the  total  num- 
ber of  cells  so  linked.  Linking  in  parallel  practically  amounts 
to  a  summation  of  all  of  the  electrode  surfaces. 

Of  course,  if  sufficient  cells  are  available,  they  can  be  divided 
into  groups  and  linked  partly  in  series,  and  partly  in  parallel. 
The  best  current-yield  is  obtained  by  linking  the  cells  in 


ELEC7RO-AXALYSIS.  77 

such  a  way  as  to  equalize,  as  nearly  as  may  be,  the  external 
and  the  internal  resistance. 

Thermopiles  are  practically  feasible  only  in  connection 
with  accumulators,  for  thermopiles  do  not  furnish  sufficient 
current  for  analytical  use.  Dynamos  can  be  constructed 
for  every  desired  current  strength  and  potential. 

A  direct  lighting  current  will  be  found  very  practical, 
especially  so  if  used  with  a  lamp-resistance  arrangement, 
which  will  be  described  later.  Among  the  most  convenient 
devices  affording  a  reliable  current  supply  are  accumulators, 
which  can  be  charged  from  a  lighting  system.  Accumula- 
tors yield  a  very  steady  current  and  almost  any  amperage 
desired  can  be  secured  by  an  adjustment  of  their  electrode 
surfaces. 

An  accumulator  may  be  defined  as  a  device  wherein  elec- 
trical energy  can  be  stored  in  the  form  of  chemical  energy 
and  from  which  electrical  energy  can  again  be  secured  at 
will.  As  a  matter  of  fact,  every  reversible  cell  may  be  re- 
garded as  an  accumulator,  in  practice,  however,  lead  accumu- 
lators are  almost  the  only  ones  used.  Plante,  in  1860,  built 
the  first  battery  of  this  kind. 

Accumulators  of  this  type  consist  of  two  plates  of  lead 
coated  with  a  layer  of  oxide  or  of  sulphate  of  lead  immersed 
in  a  20  per  cent  solution  of  sulphuric  acid.  On  passing  an 
electric  current  through  such  a  cell,  that  is  to  say,  while  charg- 
ing such  an  accumulator,  the  lead  anode  becomes  coated  with 
a  layer  of  lead  peroxide,  or  of  lead  hydrate,  while  the  cathode 
receives  a  coating  of  spongy  metallic  lead.  On  the  discharge 
of  the  accumulator,  both  of  these  layers  on  the  two  electrodes, 
the  lead  peroxide,  or  hydrate,  on  the  anode,  and  the  spongy 
lead  on  the  cathode,  are  again  transformed  into  lead  sulphate. 

Streintz  states  the  chemical  equation  of  this  change  to  be : 

PbO2  +  2H2SO4aq.  +  Pb  = 

2  PbSO,  +  2  H2O  +  aq.  +   87,000  calories. 


78  NOTES  ON  ELECTROCHEMISTRY. 

M.  Le  Blanc,  in  1895,  was  the  first  to  give  an  explanation, 
by  means  of  the  theory  of  electrolytic  dissociation,  of  the 
reactions  taking  place  in  an  accumulator.  According  to 
his  views,  the  chief  source  of  the  electromotive  force  of  a 
lead  accumulator  is  the  transformation  of  tetravalent  lead 
ions  (from  the  PbO2  in  water)  into  divalent  lead  ions.  The 
solid  lead  superoxide  replenishes  the  tetravalent  lead  ions 
which  are  consumed,  and  the  divalent  lead  ions  which  thus 
appear  enter  into  chemical  combination  with  the  sulphuric 
acid  present,  forming  sulphate  of  lead.  At  the  cathode  the 
metallic  lead  is  transformed  into  divalent  lead  ions,  and  these 
also  combine  with  sulphuric  acid  to  form  solid  sulphate  of 
lead. 

The  new  Edison  storage-battery  consists  of  a  nickel  per- 
oxide (NiO2)  anode  and  an  iron  cathode;  caustic  potash 
(KOH)  is  the  electrolyte  used. 

The  electromotive  force  of  this  accumulator  is  low,  about 
1.1  discharge  voltage,  but  it  has  certain  advantages,  for 
instance,  a  good  storage  capacity  per  unit  of  mass,  a  pro- 
nounced stability,  and  moreover,  it  can  be  quickly  charged 
and  discharged  without  injury  to  the  plates.* 

Pole-papers.  —  Whatever  the  source  of  current,  pole-papers 
so-called,  are  a  convenient  means  for  ascertaining  at  once 
which  is  the  positive  and  which  is  the  negative  pole  in  a 
given  circuit. 

These  pole-papers  are  small  strips  of  filter  paper  charged 
with  a  solution  of  some  salt  and  with  a  solution  of  some 
indicator  which  instantly  indicates  an  ionic  change  in  the 
salt  used,  solutions  of  sodium  sulphate,  and  of  phenol- 
phthalein,  for  instance. 

When  a  piece  of  filter-paper  moistened  with  the  above 
solutions  is  touched  by  the  terminal  wires  conducting  an 

*  Confer:  R<x>ber  E.  F.,  Elec.  World  and  Engineer,  1901.  Schoop, 
M.  M.,  Electro-chem.  Tnd.,  1904,  and  Sc.  Am.  Suppl.,  1905,  p.  25064. 


ELECTRO-ANALYSIS.  79 

electric  current,  the  wires  being  held  but  a  small  distance 
apart,  a  pink  mark  soon  appears  at  the  point  where  the 
negative  pole  of  the  circuit  touches  the  paper,  the  color 
being  due  to  the  reaction  of  the  phenolphthalein  with  the 
alkali  which  is  set  free  at  the  cathode. 

Current  Measurement.  —  Exact  measurements  of  the 
working  current  conditions,  of  amperage  and  voltage,  are,  of 
course,  most  essential  in  electrochemical  work.  Besides  a 
voltameter,  which  can  be  used  to  measure  current  strength 
but  which  is  principally  serviceable  in  checking  othei  meas- 
uring instruments,  an  ammeter  and  a  voltmeter  are  required. 

There  are  various  kinds  of  ammeters.  In  the  electro- 
magnetic type,  an  electric  current  is  sent  through  a  coil  of 
wire  which  surrounds  an  easily  movable  core  of  iron.  This 
iron  core  is  in  connection  with  a  pointer  which  moves  across 
a  dial,  and  the  deflection  of  this  pointer  indicates  the  strength 
of  the  current  which  passes  through  the  coil. 

The  hot-wire  ammeter  depends  for  its  action  upon  the 
heating  by  the  electric  current  of  a  very  fine  wire.  This 
wire  is  fastened  at  two  points  and  at  its  middle  is  connected 
to  another  fine  wire  which  passes  around  a  small  drum  bear- 
ing a  pointer.  A  spring,  while  at  normal  temperature,  keeps 
the  latter  wire  in  a  state  of  constant  tension;  when,  however, 
a  current  is  sent  through  the  first  wire  this  becomes  heated 
and  slackens,  the  spring  draws  on  the  second  wire  and  thus 
drum  and  pointer  are  set  in  motion.  On  account  of  its  hav- 
ing a  low  internal  resistance  an  ammeter  can  be  placed  any- 
where directly  in  the  circuit. 

Voltmeters  are  analogous  in  construction  to  ammeters;  they 
may  be  of  the  electromagnetic  or  of  the  hot-wire  type. 
If  of  the  former  description,  the  high  resistance  needed  is 
secured  by  the  use  of  a  great  number  of  windings  of  very 
fine  wire,  v/hich  reduces  the  consumption  of  current  to  a 
minimum.  In  the  hot-wire  type  the  required  resistance  is 
obtained  by  introducing  in  series  with  the  instrument  the 


80  NOTES  ON  ELECTROCHEMISTRY. 

requisite  number  of  resistance  coils;  the  greater  the  voltage 
to  be  measured,  the  more  of  these  coils  —  generally  made  of 
very  fine  wire  —  are  required.  Voltmeters,  having  a  very 
high  resistance,  are  always  placed  in  a  shunt-circuit,  the 
latter  receiving  only  a  small  fraction  of  the  current  which 
flows  along  the  main  line. 

The  resistance  of  a  wire  is  directly  porportional  to  its 
length  and  inversely  proportional  to  its  cross-section. 

If  two  paths  are  offered  an  electric  current  and  both  of 
these  paths  have  the  same  resistance,  50  per  cent  of  the  current 
travels  by  each  wire.  If,  however,  a  given  wire,  let  us  say, 
wire  A,  has  a  resistance  of  10  ohms,  and  wire  B  has  a  resist- 
tance  of  100  ohms,  then  10  per  cent  of  the  current  will  pass 
through  wire  B,  and  90  per  cent  through  wire  A. 

A  voltmeter  can  also  be  conveniently  used  as  an  ampere- 
meter provided  that  a  known  resistance  is  introduced  into 
the  electric  circuit  and  that  the  terminals  of  the  voltmeter 
are  attached  to  this  resistance. 

As,  E  =  CR, 


hence,  if  R  is  known  and  E  is  ascertained  by  a  voltmeter, 
C  can  be  determined  at  a  glance. 

If  a  resistance  of  1  ohm  is  used  in  the  circuit,  the  values 
indicated  by  the  voltmeter  read  directly  in  amperes,  for 

1  volt 

1  ampere  =  -  —  r  — 
1  ohm 

If  the  resistance  introduced  is  0.1   ohm,   then  each    unit 
indication  of  the  voltmeter  represents  10  amperes,  for 

1  volt 
10  amperes  = 


EL  EC  TRO-A  NA  L  YSIS,  81 

If  the  resistance  employed  is  10  ohms,  each  unit  indication 
in  the  scale  represents  0.1  ampere,  for 

1  volt 

0.1  ampere  =  ^-r — r —  • 
10  ohms 

It  is  therefore  possible,  by  the  proper  selection  of  resistance, 
to  obtain  a  very  wide  range  of  current  strength. 

Current  Regulation.  ---  The  regulation  of  an  electrical  cur- 
rent used  for  electrolytical  purposes  can  be  achieved  by  the 
introduction  of  the  proper  amount  of  resistance  into  the 
circuit,  and  by  a  regulation  of  the  distance  between  the  elec- 
trodes in  the  electrolyte. 

The  so-called  resistance  boxes  usually  consist  of  coils  or 
spirals  made  of  German-silver  wire,  or  of  some  other  alloy. 
Among  alloys  specifically  made  for  this  purpose  are  nick- 
eline,  constantan,  platinoid,  and  manganin.  Mariganin  is 
an  alloy  of  manganese,  nickel  and  copper;  it  has  a  very  high 
resistance  and  a  very  small,  negative  coefficient  of  tempera- 
ture, and  it  is  therefore  especially  valuable  for  the  manufac- 
ture of  electrical  apparatus,  where  constancy  of  resistance 
at  various  temperatures  is  called  for. 

A  current  passing  through  a  wire  heats  the  wire,  and  in 
consequence  the  resistance  rises.  For  some  purposes  it  is 
very  desirable  to  avoid  such  a  variation  in  the  resistance, 
and  in  such  instances  use  can  be  made  to  advantage  of  an 
alloy  that  has  a  low  temperature  coefficient. 

Platinoid  is  an  alloy  of  this  description;  its  increased  resist- 
ance through  a  range  of  100°  C.  (from  0°  to  100°  C.) 
is  only  2.09  per  cent,  whereas  silver,  annealed  or  hard-drawn, 
shows  a  rise  of  40  per  cent,  and  annealed  copper  a  rise  of 
almost  43  per  cent. 

Another  simple  and  serviceable  device  for  introducing 
resistance  into  an  electric  circuit  is  the  lamp-bank.*  Alamp- 

*  Consult  Hopkins,  liber,  cit.,  p.  13. 


82  NOTES  ON  ELECTROCHEMISTRY. 

bank  is  made  by  arranging  a  number  of  lamp-sockets  partly 
in  parallel,  partly  in  series,  upon  a  slab  of  slate  or  marble, 
and  then  inserting  the  necessary  number  of  lamps  properly 
grouped  to  give  the  desired  resistance.  The  current  may 
be  conveniently  taken  from  a  direct  lighting  circuit. 

When  lamps  are  arranged  in  parallel,  their  combined  re- 
sistance is  equal  to  the  resistance  of  one  lamp  divided  by 
the  number  of  lamps  in  parallel;  when  arranged  in  series 
their  combined  resistance  is  equal  to  the  resistance  of  one 
lamp  multiplied  by  the  number  of  lamps  in  series. 

Assume,  for  instance,  that  eight  16  candle-power  lamps 
are  available  and  that  the  lamp-board  is  arranged  in  such  a 
manner  that  these  lamps  can  be  used  either  in  parallel  or  in 
series. 

Let  E  =  110  volts, 

R  -  220  ohms, 

and  have  the  8  lamps  arranged  in  parallel, 
therefore,  in  this  instance, 


i.e.,  4  amperes  would  pass  through  the  lamps  thus  grouped 
If  the  8  lamps  were  arranged  in  series, 

110  110        0.062. 


220  X  8       1760 

i.e.,  only  0.062  ampere  would  flow  through  the  combination. 

It  is  thus  evident,  that  by  grouping  some  of  the  lamps  in 
parallel  and  some  in  series,  and  by  using  lamps  of  different 
resistances,  almost  any  desired  amperage  may  be  secured. 

Of  course,  the  introduction  of  resistance  into  the  circuit 
in  such  a  manner  is  the  reverse  of  economical;  a  110- volt 


ELECTRO-ANALYSIS.  83 

current  cut  down  to,  say,  4  volts,  renders  no  more  effective 
service  than  the  current  of  a  4- volt  generator  directly  applied. 
The  actual  current  strength  in  any  electrolytic  circuit  is 
determined  by  the  formula: 


C  =  -  ° 

in  which: 

E   —  voltage  of  the  current, 
e     =  counter-voltage, 
R   =  resistance  of  cell, 

Rl  =  resistance  of  the   conductor  (the  leads),  be- 
tween generator  and  cell. 

In  electrochemical  analysis,  however,  the  voltage  is  gen- 
erally measured  directly  between  the  terminals  of  the  cell, 
that  is,  the  value  of  R  only  is  sought  and  the  value  Rl  not 
taken  into  account. 

The  resistance  of  an  electrolytic  cell  may  also  be  calcu- 
lated by  the  formula: 

R       ~          T1       /T 

E.S 
in  which, 

D  =  distance,   in    centimeters,    between    the    electrodes  — 

these  being  assumed  to  be  perfectly  parallel, 
p  =  the  specific  resistance  of  the  electrolyte, 
E.S.  =  electrode  surf  ace,  i.e.,  the  area  in  square  centimeters  of 
each  electrode. 

If  there  are  three  plates  and  the  current  flows  from  the 
central  plate  to  each  of  the  other  two,  then  the  value  of  R 
is  found  as  above  for  either  side,  and  the  combined  resistance 
equals  one-half  of  the  value  thus  found. 

The  resistance  of  electrolytes  varies  with  their  chemical 
nature,  with  their  concentration,  and  with  the  temperature. 
An  increase  in  temperature  markedly  decreases  the  resist- 


84  NOTES  ON  ELECTROCHEMISTRY. 

ance   of   electrolytes;   in    this   respect   electrolytes   resemble 
the  behavior  of  carbon. 

The  cross-section  of  a  wire,  in  square  millimeters,  for  in- 
stance, of  a  copper  wire  used  for  conducting  an  electric  cur- 
rent, is  calculated  by  the  formula : 

r  „  _  L.C.  0.01687 
D.P. 

in  which: 

C.S.  —  cross-section  in  square  millimeters, 

L  =  total  length  of  conducting  wire  —  that  is,  the  sum 
of  the  lengths  of  wire  leading  from  the  source 
of  current  supply  and  back, 
C  —  the  maximum  current  strength  to  be  conducted  — 

expressed  in  amperes, 

Z).  P.  =  the  maximum  permissible  drop  in  potential  —  ex- 
pressed in  volts, 

0.01687  =  specific  resistance  of  copper,  i.e.,  the  resistance  of 
a  copper  wire  1  meter  long  and  1  square  milli- 
meter in  cross-section. 

The  cross-sections  of  round  wires  are  very  often  given  in 
circular  mils.  A  mil  is  the  one-thousandth  part  of  an  inch 
(=  0.0254  millimeter).  A  circular  mil  is  the  area  of  a  circle 
the  diameter  of  which  is  one  mil;  a  circle  having  a  diameter 
d  has  an  area  of  d2  circular  units.  One  circular  mil  is  equal 
to  0.000506709  square  millimeter,  and  one  square  millimeter 
is  equal  to  1973.52  circular  mils. 

In  calculating  the  cross-sections  of  the  conducting  wires 
between  the  sources  of  supply  and  the  working-station  a 
safety-margin  of  from  20  to  25  per  cent  over  and  above  the 
amount  calculated,  should  be  allowed. 

Electrodes.  —  The  electrodes  used  in  electro-analytical 
work  are  usually  made  of  platinum.  The  cathode  may, 
according  to  conditions,  be  either  a  crucible,  a  dish,  a  flag 
or  foil,  a  cone,  or  a  cylinder. 


ELEC  TRO-A  NA  L  YSIS.  85 

If  a  dish  be  used  it  is  generally  selected  to  hold  from  150 
to  200  cubic  centimeters;  whatever  the  shape  chosen,  the 
utmost  care  must  be  taken  to  have  the  surface  which  is  to 
receive  the  electrolytic  deposit  perfectly  smooth  and  abso- 
lutely clean  and  bright,  above  all,  not  a  trace  of  oil  or  of 
any  other  fatty  matter  may  be  present. 

The  anode  may  be  a  plain  foil  or  a  flag,  a  wire  to  the  end 
of  which  a  small  disk  has  been  soldered,  a  spiral  coil,  or  a 
cylinder.  To  whichever  shape  preference  is  to  be  given 
will,  to  a  certain  extent,  be  determined  by  the  current  den- 
sity required. 

A  convenient  electrode  support  consists  of  an  upright  rod 
or  bar  of  glass  to  which  a  metallic  ring  and  a  metallic  bar 
are  attached  in  such  a  way  that  these  can  readily  be  set  in 
any  position  desired.  The  metallic  ring  is  intended  for  the 
support  of  the  cathode  —  a  platinum  dish  for  instance  — 
and  is  in  connection  with  the  negative  pole  of  the  current. 
The  anode  is  fastened  to  the  metal  bar  and  this  is  connected 
with  the  positive  pole  of  the  electric  current. 

As  warm  electrolytes  are  superior  conductors,  the  plati- 
num dish,  which  serves  as  the  cathode,  may  conveniently  be 
placed  on  a  thin  plate  of  asbestos  and  heated  by  a  small 
gas-flame,  electrically,  or  in  some  other  manner.  Various 
analyses,  of  course,  demand  various  temperature  conditions, 
but  it  seems  that,  as  a  rule,  50°  C.  should  not.be  exceeded. 

The  use  of  a  stationary  anode  generally  entails  the  em- 
ployment of  a  weak  current  and  hence  necessitates  the  use 
of  considerable  time  for  the  electrodeposition  of  some  metals. 
This  is  due  to  the  fact  that  concentration  changes  are  set 
up  in  the  solution,  a  decrease  in  the  concentration  of  the 
cathions  becoming  noticeable  near  the  cathode  as  the  depo- 
sition progresses.  This  difficulty  can  be  avoided  by  the 
use  of  a  rotating  anode  driven  by  an  electric  or  water  motor 
and  revolving  perhaps  from  30  to  130  times  per  minute.  By 
this  means  the  concentration  of  the  electrolyte  is  kept  uni- 


86  NOTES  ON  ELECTROCHEMISTRY. 

form,  a  stronger  current  can  be  employed,  and,  in  conse- 
quence, considerable  time  be  saved. 

It  is  also  possible  to  make  use  of  a  rotating  cathcde,  a 
platinum  crucible,  for  instance,  answers  this  purpose  well.* 
Giving  such  a  cathode  a  speed  of  rotation  of  from  600  to 
700  revolutions  per  minute,  and  working  with  a  normal 
current  density  of  from  5.0  to  6.6  amperes,  15  to  30  minutes 
will  suffice  for  an  electrodeposition  which  ordinarily  would 
require  hours  for  its  completion. 

In  calculating  electrode  areas  it  is  customary  to  measure 
the  surfaces  of  the  electrodes  only  to  the  extent  that  the 
same  are  in  contact  with  the  electrolyte. 

Formula;  for  Calculation  of  Electrode  Areas. 

d  =  diameter,  IT  =  3.1416. 

r  =  radius. 

Circumference  of  a  circle:  d  x  •*, 

r  X  2,1-, 
Area  of  a  circle  :  cP  x  .7854, 


Surface  areas. 

1.  Foil  or  flag:     Height  x  length. 

2.  Cone  or  pyramid:  Product  of  perimeter  of  base  by  half 

the  slant  height,  plus  the  area  of  the  base. 

3.  Open-end    cylinder   or   prism:    Perimeter   of   one   end   x 

height. 

4.  Closed-end   cylinder  or  prism:   Perimeter  of  one   end   x 

height,  plus  twice  the  area  of  one  end. 

5.  Interior  surface  of  a  dish  (curve-surface  of  a  segment  or 

a  zone  of   a  sphere)  :  Diameter  of  sphere  x  height  of 
segment  or  zone   X  rr. 

*  Am.  Journal  of  Science,  Vol.  15,  p.  320. 


ELECTRO-ANALYSIS.  87 


6.    Cylindrical  gauze:  «•« 

d  —  diameter  of  wire, 

n  =  number  of  meshes  per  square  centimeter, 

"11    (  °f  gauze  used. 
b  =  width  ) 

Current  Density.  —  This  term,  as  previously  stated,  desig- 
nates the  ratio  of  the  electrode  area  to  the  flow  of  current. 
It  is  customary  to  term  the  current  strength  per  100  cm2, 
(one  square  decimeter,  1  dm2)  of  electrode  surface,  the 
normal  density  of  current,  and  this  value  is  symbolized  by 

For  instance,  N.D.m  •-=  0.5  signifies  that  the  current  flow 
for  every  100  square  centimeters  of  electrode  surface  is 
0.5  ampere. 

Let,  D  =  current  density, 

C  =  current  strength, 

E.S.=  electrode    surface   on  which   electro-deposi- 
tion takes  place. 

C 
then,  D  -  ^~-, 

Q 

and  N.D.100  = 


If  the  N.D.iw  and  the  electrode  surface  are  known,  the  cur 
rent  strength  is  readily  calculated  by  the  formula, 


For  instance,  let: 

C  =  5  amperes, 
E.S.=  180  cm?. 

*  Winkler  :  Berichte,  Vol.  32,  p.  2192. 


88  NOTES  ON  ELECTROCHEMISTRY. 


Then:  D--  0.028, 


1  80 
and,  N.D.m=  5    -  —  =  2.8. 

1  SO 
ard,  C=  2.8  X  —  =  5.0. 

The  current  density  may  either  be  the  same  or  unlike  at 
the  two  electrodes.  If  both  electrode  areas  are  alike,  a 
given  current  strength  will,  of  course,  ensure  identical  cur- 
rent density  at  both  electrodes.  A  given  current  strength 
passing  from  a  small  electrode  area  naturally  means  a  high 
current  density  at  that  electrode.  Thus  let: 

C  =  5.0 
E.S.  =  1.0 

then,  D  =  -  --=  5.0 

The  same  current  strength  passing  form  a  large  electrode 
surface  determines  a  low  current  density  at  that  electrode. 

Thus:  C  =  5, 

E.S.=  100, 

Z>  -          =  0.05. 


All  electrochemical  operations  are  greatly  influenced  by 
the  current  density. 

Records.  —  The  records  of  all  electrochemical  work  should 
be  kept  in  such  a  manner  as  to  permit  of  the  exact  repeti- 
tion of  such  work  at  any  time.  What  the  specific  data  of 
such  record  should  be,  is,  of  course,  in  a  large  measure  deter- 
mined by  the  nature  of  the  work  under  consideration. 


ELEC  TRO-A  NA  L  YSIS.  89 

In  all  cases,  however,  such  record  should  include  data  of 
the  source  of  the  current  used,  the  time  during  which  the 
current  passes,  the  material  of  which  the  electrodes  consist, 
the  distance  between  the  electrodes  in  the  working -cell, 
the  active  area  of  the  electrodes,  the  voltage  and  amperage 
employed,  the  current  density,  the  character  of  the  elec- 
trolyte, its  temperature  throughout  the  reaction,  and,  in 
addition,  any  specific  phenomena  which  may  be  noticed  at 
anode  and  cathode. 

Resum^. —The  principal  facts  to  be  borne  in  mind  in 
electro-analytical  work  and  in  the  study  of  electrolytic 
processes  are  the  following: 

Each  ion  bears  a  definite  charge  of  electricity.  The  ionic 
charge  for  a  monovalent  gram  ion  is  =  96,540  coulombs. 
The  ionic  charge  is  directly  proportional  to  the  valence  of 
the  ion  and  is  the  same  for  all  ions  of  the  same  valence, 
whether  such  an  ion  be  an  individual  ion  or  a  complex  ion. 
Thus,  the  cathions  silver  and  sodium  bear  equal  charges  of 
positive  electricity,  while  the  anions,  chlorine,  iodine,  and 
NO3  bear  equal  charges  of  negative  electricity. 

The  amount  of  an  element  deposited  or  liberated  electro- 
lytically  is  proportionate  to  the  current  used.  A  given 
current  will  deposit  or  set  free  of  various  elements,  amounts 
directly  proportionate  to  the  atomic  weights  of  those  ele- 
ments and  inversely  proportionate  to  their  valence. 

Thus,  taking  the  atomic  weight  of  silver,  107.93,  as  the 
basis,  the  number  of  grams  of  any  element  set  free  or  de- 
posited by  one  ampere  hour  is  equal  to : 


0.037291  x     atomicweiSht 


change  of  valency 

For  instance,  of  copper  there   will  be  deposited  from  a 
solution  of  cupric  chloride,  CuCl2: 


90  NOTES  ON  ELECTROCHEMISTRY. 

63.6 


0.037291  X 


2 
0.037291    x  31.8  =  1.1858  grams. 

One  ampere  hour  will  thus  deposit  of: 
Silver,    .   .   .   4.0248  grams, 
Copper  (from  a  cupric  salt)  1.1858  grams, 
and  these  values  are  in  the  same  ratio  as  the  respective 

(107.93)                             (63.6) 
chemical  equivalents  of  silver and  of   copper 

i.e.  as  107.93  and  31.8. 

Great  stress  must  also  be  laid  on  having  the  current  used 
sufficient  in  amount,  in  other  words,  the  current  density 
must  be  sufficiently  large  so  that  the  rate  at  which  a  metal 
is  precipitated  is  greater  than  the  rate  at  which  it  tends  to 
redissolve  in  the  solution  from  which  it  is  being  deposited. 
This  is  proportionate  to  the  area  of  the  surface  of  the  elec- 
trode at  which  the  deposition  occurs,  hence  the  amount  of 
current  per  unit  of  surface  area,  the  current  density,  is  a 
factor  of  prime  importance. 

While  the  various  chemical  elements  are  set  free  in  equiv- 
alent amounts  at  the  electrodes,  it  is  necessary  to  remember 
that  the  amount  of  electrical  energy  requisite  to  effect  an 
electrolytic  decomposition  varies  with  the  nature  of  the 
chemical  combination  to  be  decomposed. 

The  minimum'  dissociation  voltage,  the  critical  voltage, 
differs  for  each  element  and  is  characteristic  of  it.  Advan- 
tage is  taken  of  this  fact  to  separate  different  metals  ana- 
lytically. For  instance,  in  passing  a  current  through  a  solu- 
tion of  several  metals,  the  metal  having  the  lowest  critical 
voltage  will  be  deposited  first;  if  the  voltage  be  then  in- 
creased, metal  after  metal  will  be  precipitated,  and  the  metal 
having  the  highest  critical  voltage  will  be  the  last  one  to  be 
deposited. 


ELECTRO-A  NALYSIS.  91 

As  a  rule,  thermal  units  are  employed  to  measure  the 
energy  evolved  or  absorbed  in  the  formation  of  chemical 
compounds.  As  previously  stated,  the  thermal  units  em- 
ployed are  either  calories,  or,  Calories,  the  iormer  repre- 
senting the  amount  of  heat  needed  to  raise  the  temperature 
of  one  gram  of  water  one  degree  C.,  from  15°  C.  to  16°  C.; 
the  latter,  the  amount  of  heat  needed  to  raise  the  tempera- 
ture of  one  kilogram  of  water  one  degree  Centigrade.* 

To  effect  an  electrolytic  deposition  of  a  chemical  sub- 
stance in  aqueous  solutions,  an  amount  of  electrical  energy 
must  be  used  equivalent  to  the  number  of  calories  involved 
in  the  formation  of  the  compound  to  be  electrolysed. 

The  unit  of  electrical  energy  is  the  joule;  one  joule  is 
equivalent  to,  practically,  0.24  calorie,  or  to  0.00024  Calorie. 
When  the  heat  of  formation  of  an  electrolyte  is  known,  this 
value  divided  by  0.24  equals  the  joules  required  to  effect  its 
electrolysis. 

1  joule  =  1  coulomb  x  1  volt,  therefore,  the  number  of 
joules  divided  by  96,540  —  or  a  multiple  thereof  —  repre- 
sents the  critical  voltage,  i.e.  the  minimum  voltage  neces- 
sary to  effect  the  desired  electrolysis. 

The  fundamental  facts  then  to  be  remembered  are,  that  it 
always  requires  a  definite  quantity  of  energy  to  effect  the 
electrolysis  of  a  given  substance  at  a  given  temperature,  and 
that  such  electrolysis  can  only  be  effected  by  the  use  of  a 
definite  minimum  voltage. 

In  passing  upon  the  efficiency  of  any  electrolytic  process, 
it  is  necessary  to  pay  due  regard  to  both  current  efficiency 
and  to  energy  efficiency.  In  other  words,  it  is  necessary  to 
determine  how  closely  the  weight  of  the  product  obtained, 
compares  with  the  weight  of  the  product  theoretically  pro- 
ducible by  the  number  of  coulombs  used;  furthermore,  the 
weight  of  the  product  obtained  should  be  compared  with 

*  Confer:  Joseph  W.  Richards'  "  Electrochemical  Calculations,"  Jour- 
nal Franklin  Im-tftute,  1900,  p.  131. 


92  NOTES  ON   ELECTROCHEMISTRY. 

the  amount  theoretically  obtainable  by  a  perfect  utilization 
of  the  total  number  of  joules  employed. 

Thus,  if   the  current  efficiency  in  a  given   process  is  90% 
and  the  voltage  efficiency  is  60%,  then  the  energy  efficiency  is 

90  x  60 


100  X  100 


54%. 


In  obtaining  the  electrodeposition  of  an  element  from  a 
compound,  it  is  a  great  advantage  to  effect  such  electro- 
deposition  from  an  ows-salt  rather  than  from  an  re-salt  for 
the  reason  that  the  ous  compound  compared  with  the  ic  com- 
pound, contains  twice  the  amount  of  the  metallic  constitu- 
ent per  unit  weight  of  the  non-metalic  radicle  with  which 
it  is  combined.  In  consequence  an  electric  current  of  a 
given  amperage  will  deposit  twice  as  much  metal  from  an 
ous  salt  as  it  will  from  an  ic  salt,  and  although  a  somewhat 
higher  voltage  is  required  in  the  former  case,  this  is  more 
than  compensated  for  by  the  increased  output  obtained. 


CHAPTER   VI. 
ELECTROTECHNOLOGY. 

Literature:  BLOUNT,  B.:  "Practical  Electrochemistry."  New  York, 
1901.  FERCHLAND,  P.:  "Grundriss  der  Reinen  und  Angewandten 
Elektrochemie. "  Halle,  A.  S.,  1903.  FOERSTER,  F.:  "Elektro- 
chemie  Wiisseriger  Losungen."  Leipzig,  1905.  HABER,  F. : 
"Grundriss  dor  Technischen  Elektrochemie."  Miinchen,  1898. 
LOEB,  W.:  "Elektrochemie  der  Organischen  Verbindungen." 
Halle,  A.  8.,  1905.  MOISSAN,  H.  (translated  by  Lenher,  W.) :  "The 
Electric  Furnace."  New  York,  1905.  NERNST,  W.  and  BOR- 
CHERS,  W.:  "Jahrbuch  der  Elektrochemie."  Halle,  A.  S.,  Vol.  X, 
1905.  PETERS,  F.:  "Angewandte  Elektrochemie."  Leipzig,  1897. 
PETERS,  F. :  "Elektrochemische  Technik."  Vol.  IV.  Gross-Lich- 
terfelde  West,  1905.  SLOANE,  T.  O'C.  :  "Electricians'  Handy 
Book."  New  York,  1905.  VOGEL,  F.  and  ROSSING,  A.:  "Hand- 
buch  der  Elektrochemie  und  Elektrometallurgie."  Stuttgart, 
1891.  WRIGHT,  J.:  "Electric  Furnaces  and  their  Industrial  Ap- 
plications." New  York,  1905. 

Introduction.  —  The  applications  of  electrochemistry  are 
•so  numerous  that  it  will  he  desirable  to  devise  some  sort  of 
a  classification  in  order  to  gain  a  general  survey  of  the  sub- 
ject. 

In    so  doing,  two    principal    groups  may  be  established: 

I.    Direct  action  processes. 
II.    Indirect  action  processes. 

In  the  first  of  these  groups  there  must  be  counted  all  pro- 
cesses in  which  the  electric  current  acts  directly;  in  the  second, 
all  processes  in  which  the  electric  energy  suffers  partial  or 
entire  transformation  into  some  other  form  of  energy  before 
being  applied  to  the  work  required.  The  first  group  would 
thus  embrace  all  processes  of  electrodeposition  from  solu- 
tions —  metals  and  non-metals;  the  second  group  would 

93 


94  NOTES  ON  ELECTROCHEMISTRY. 

include   electrodeposition    from    fused    electrolytes,    and    all 
electrothermic  processes. 

For  the  sake  of  convenience,  the  following  sub-divisions 
can  be  made: 

A.  Electro-inorganic  Processes. 
I.    Direct  Action  Processes. 

Electrodeposition  from  solution. 
Electroplating. 

Chlorine  and  Alkali-hydrates. 
II.    Indirect  Action  Processes. 

Electrodeposition  from  fused  electrolytes. 
Electrothermic  processes. 

B.  Electro-organic  processes. 
I.    Direct  action  processes. 

II.    Silent  discharge  processes. 
III.    Electro-osmosis. 

A.  I.    DIRECT  ACTION  PROCESSES. 
Electrodeposition  from  Solution. 

Copper.  —  Although  several  processes  have  been  devised 
for  obtaining  copper  from  its  ores  by  the  aid  of  the  electric 
current,  not  one  of  these  processes  has  attained  to  any  great 
importance  in  commercial  practice. 

In  one  of  the  earliest  of  these  processes,  that  devised  by 
Marchese  in  1884,  the  ore  was  prepared  and  brought  into  the 
form  of  an  impure  sulphide,  consisting  of  copper,  lead,  and 
iron.  This  compound  was  cast  into  anodes  and  subjected 
to  electrolysis  in  a  sulphuric  acid  solution. 

In  later  processes  solvents  are  used  to  extract  the  copper 
from  its  ore,  and  the  solutions  thus  obtained  are  subjected  to 
electrolysis,  insoluble  anodes  being  employed. 

Thus,  in  the  Siemens-Halske  process  the  solvent  employed 
for  extracting  the  copper  present  as  sulphide,  is  an  aqueous 


ELECTROTECHNOLOGY.  95 

solution  of  ferric  sulphate.  In  effecting  the  extraction  of 
the  copper  this  ferric  sulphate  becomes  reduced  to  the  fer- 
rous condition,  but  is,  in  turn,  restored  to  its  original  condi- 
tion by  undergoing  oxidation  in  the  anode  section  of  the 
trough  after  the  metallic  copper  has  been  precipitated  from 
its  sulphuric  acid  solution  at  the  cathode.  Carbon  anodes 
are  generally  used. 

In  the  Hoepfner  process,  the  ore  is  not  subjected  to  any 
preliminary  roasting;  the  copper,  in  the  form  of  cuprous 
sulphide,  is  leached  out  by  means  of  a  sodium  chloride  solu- 
tion containing  cupric  chloride,  cuprous  chloride  is  thus 
formed  and  is  kept  in  solution  by  means  of  the  sodium  chlor- 
ide which  is  present.  The  electrolytic  troughs  are  separated 
into  anode  and  cathode  chambers  by  means  of  diaphragms  and 
the  electrolyte  is  first  passed  through  the  cathode  chambers 
where  most  of  the  copper  is  precipitated.  In  the  anode 
chamber  the  remaining  cuprous  chloride  is  changed  to  the 
cupric  form,  and  the  process  is  thus  made  a  continuous  one. 

While  the  extraction  of  copper  from  its  ores  by  electro- 
lytic action  is  as  yet  not  well  developed,  the  electrolytic 
refining  of  copper  is  one  of  the  most  important,  if  not  the 
most  important,  application  of  electrochemistry. 

The  first  suggestion  of  electrolytic  copper  winning  is 
credited  to  Becquerel  (1836);  the  first  obtaining  of  electro- 
lytic copper  on  the  commercial  scale  to  James  B.  Elkington 
of  England  (1865). 

Two  systems  are  employed  in  copper  refining,  the  series 
system  and  the  multiple  system;  the  latter  is  the  older. 

In  the  multiple  system  each  anode  is  connected  with  the 
conductor  from  the  positive  pole  of  the  electric  current;  each 
cathode  with  the  conductor  from  the  negative  pole. 

In  the  series  system,  due  to  E.  S.  Hayden  of  Connecticut, 
only  one  end-anode  in  each  tank  is  connected  with  the  posi- 
tive pole  and  at  the  opposite  end  only  one  cathode  is  con- 
nected with  the  negative  pole.  Between  these  electrodes, 


96  NOTES  ON  ELECTROCHEMISTRY. 

copper  plates  are  set  in  an  upright  position;  the  circulation 
of  the  electrolyte  may  be  maintained  by  compressed  air  or 
by  some  other  device. 

The  plates  of  crude  copper  which  serve  as  anodes,  usually 
have  a  surface  of  from  55  to  75  square  decimeters,  and  are 
from  2  centimeters  to  4  centimeters  thick;  the  cathodes  con- 
sist of  thin  plates  or  foils  of  pure  copper.  The  distance  be- 
tween the  electrodes  is  generally  maintained  at  from  2.5  to 
5.0  centimeters,  the  electrolyte  used  is  a  solution  of  sulphate 
of  copper  acidified  with  sulphuric  acid.  The  voltage  em- 
ployed is  low,  probably  not  exceeding  one-half  volt. 

In  preparing  the  electrolyte,  copper  sulphate  solution  and 
sulphuric  acid,  care  must  be  taken  to  insure  a  solution  rich 
in  copper,  and  to  have  it  contain  sufficient  sulphuric  acid  to 
prevent  the  formation  of  hydratcd  cupric  oxide;  on  the  other 
hand,  care  must  be  taken  to  guard  against  an  excess  of  sul- 
phuric acid,  as  this  would  cause  the  liberation  of  hydrogen  at 
the  cathode  in  the  place  of  copper.  The  temperature  of  the 
electrolyte  is  advantageously  held  at  about  33°  C.  to  37°  C. 

The  question  of  current  density  is  of  course  a  very  impor- 
tant one,  the  value  of  ND100  ranges  from  1.3  to  possibly  as 
high  as  4.00.  However,  too  high  a  current  density  must  be 
avoided,  as  this  causes  the  copper  to  be  deposited  in  uneven 
masses,  possessing  but  poor  coherence.* 

The  tanks  in  which  the  electrolytic  deposition  takes  place 
are  generally  lined  with  lead ;  there  are  often  several  hundred 
of  these  in  a  plant.  When  in  the  course  of  operation  the 
anodes  have  been  reduced  to  thin  sheets,  the  process  is  inter- 
rupted, the  anodes  are  removed  and  re-smelted,  the  cathodes 
are  likewise  removed  and  recast,  and  the  anode-slime,  or 
mud,  as  it  is  termed,  is  subjected  to  separate  treatment  for 
the  obtainment  of  the  precious  metals  which  occur  therein 
whenever  such  are  present  in  the  copper  ores  worked. 

*  Consult:  S.  Cowper-Coles,  Trans.  Faraday  Society,  1905,  p.  215, 
and  L.  Addicks,  Journal  Franklin  Jnst.,  1905,  p.  421. 


OF  THF 

UNIVERSIT 

ELECTROTECHNOLOGY. 

Among  the  impurities  frequently  found  associated  with 
copper  are  iron,  cobalt,  nickel,  zinc,  gold,  platinum,  silver, 
bismuth,  antimony,  arsenic,  and  lead.  Of  these  impurities 
iron,  cobalt,  nickel,  and  zinc  dissolve  in  the  electrolyte,  but 
are  not  apt  to  be  precipitated  on  the  cathode  under  the  cur- 
rent conditions  employed  for  the  electrolytic  deposition  of 
the  copper. 

Among  the  impurities  found  in  the  anode-slime  are  gold 
and  silver.  In  some  copper  ores  the  amount  of  these  metals 
recovered  from  the  anode-slime  is  very  considerable.  For 
instance,  an  analysis  given  by  E.  Keller*  shows  the  amount 
of  the  precious  metals  contained  in  an  anode-slime  derived 
from  a  copper  ore  mined  near  Butte,  Montana,  to  have  been 
as  high  as  0.2%  to  0.3%  of  gold  and  53%  to  55%  of  silver. 

The  purity  of  copper  electrolytically  refined  is  very  high, 
frequently  ranging  up  to  99.95%  and  99.99%. 

To  illustrate  the  manner  in  which  the  output  of  an  electro- 
lytic copper  refining  plant  can  be  calculated,  assume  that  the 
normal  current-density  employed  is  one  ampere  per  square 
decimeter,  i.e.,  ND100  =  1.00.  Further,  assume  that  the 
active  anode  surface  in  one  vat  is  372  square  decimeters,  then 
each  vat  requires  372  amperes. 

The  weight,  in  milligrams,  of  any  element  set  free  by  one 
coulomb  of  electricity  is  equal  to  its  atomic  weight  divided 
by  its  valence  and  multiplied  by  0.01036,  the  electrochemi- 
cal equivalent  of  hydrogen. 

Thus,  one  coulomb  will  deposit  from  a  cupric  salt  solu- 

no  c 

tion   — -   x  0.01036  =  0.329448   milligram,    say   0.33    milli- 
gram of  metallic  copper. 

One  ampere-hour  equals  3600  ampere-seconds,  hence,  one 
ampere  in  one  hour  will  deposit  0.33  X  3600  =  1.188  grams 
of  copper  and  in  24  hours  1.188  X  24  =  28.5120  grams. 

*  Journal  of  American  Chemical  Society,  1897,  p.  778. 

-. 


98:  NOTES  ON  ELECTROCHEMISTRY. 

In  the  same  period  372  amperes  will  deposit  28.5120  x  372 
=  10,606  grams,  or,  10.606  kilograms  of  copper.  This  amount 
multiplied  by  the  number  of  vats  in  use,  will  of  course  give 
the  total  output  in  24  hours. 

As  to  the  question  of  energy  consumption,  assume  a  maxi- 
mum current  efficiency,  and  assume  that  the  drop  in  poten- 
tial is  0.25  volt.  Each  vat  will  thus  require  0.25  x  372  =  93 

93 
watts,  and  this  corresponds  to  - — =  0.125  H.P. 

One  H.P.  will  therefore  deposit  in  twenty-four  hours, 
0.125:1.0::  10.606:  x  -  84.85  kilograms  of  copper,  and  a 
plant  of  5000  H.P.  would  therefore  yield  84.85  X  5000  = 
424,250  kg.  of  copper  in  twenty-four  hours. 

Silver.  —  The  principles  underlying  the  process  of  re- 
fining silver  electrolytically,  and  especially  adapted  to 
its  separation  from  gold  and  copper,  were  worked  out  by 
Moebius. 

The  electrolyte  used  is  a  solution  of  nitrate  of  silver  con- 
taining about  1%  of  silver  and  from  0.1  to  1%  of  free  nitric 
acid.  The  cathodes  consist  of  pure  silver  foil  and  these 
receive  a  very  light  coating  of  oil  in  order  to  permit  of  a 
more  ready  removal  of  the  crystals  of  silver,  the  form  in  which 
the  silver  separates  from  the  electrolyte  under  proper  current 
conditions.  The  anodes  are  made  of  crude  silver,  contain- 
ing about  95%  of  this  metal,  the  balance  generally  consisting 
of  gold,  platinum,  and  copper. 

As  stated,  the  silver  separates  in  a  crystalline  condition 
and  the  removal  of  these  crystals  is  effected  by  wooden  arms 
which  are  kept  in  slow  movement,  constantly  freeing  the 
cathodes  from  these  crystals;  if  this  were  not  done  the  crystals 
would  readily  grow  to  the  anodes  and  in  this  manner  of  course 
establish  a  short  circuit.  The  anodes  are  inclosed  in  a 
sheathing  of  canvas  and  in  this  the  anode-slime  accumulates. 
This  anode  residue  is  of  course  separately  treated  for  the 
recovery  of  the  precious  metals  it  contains. 

(I/ 


ELECTROTECHNOLOGY.  99 

The  current  conditions  generally  employed  for  the  electro- 
lytic refining  of  silver  are,  voltage  =  1.5  and  ND100  =  2.5. 

Gold.  —  The  extraction  of  crude  gold  from  its  ores  is  gen- 
erally effected  either  by  the  use  of  mercury,  by  one  of  the  so- 
called  chlorination  processes  —  wherein  chlorine  is  the  active 
agent,  or  else  by  use  of  potassium-cyanide  acting  in  the 
presence  of  atmospheric  oxygen. 

Potassium-cyanide  is  the  reagent  employed  in  the  Siemens- 
Halske  process  and  the  gold  is  recovered  electrolytically  from 
the  cyanide  solution.  The  cyanide  liquor  contains  not  more 
than  0.05%  of  potassium  cyanide.  The  anodes  are  generally 
made  of  iron,  although  carbon,  Achcson-graphite,  and  lead- 
per-oxide  anodes  are  also  used;  they  are  inclosed  in  bags  of 
canvas  or  linen. 

The  cathodes  are  made  of  lead,  and  when  sufficient  gold 
has  been  deposited  on  them  they  are  cupeled  and  the  gold 
obtained.  The  crude  gold  thus  secured  contains  about 
85%  to  90%  of  pure  gold;  this  is  subjected  to  electrolytic 
refining  while  the  lead  recovered  is  reduced,  recast,  and  again 
used  for  cathodes.  The  current-de  isity  employed  is  very  low. 
ND100  ranges  from  about  0.003  to  0.005;  the  voltage  from 
about  1.75  to  2.00  volts. 

In  Wohwill's  process  for  the  electrolytic  refining  of  gold 
the  anodes  of  crude  gold  are  placed  into  a  hot  solution  of 
hydrogen  auric  chloride  (H  Au  C14)  containing  hydrochloric 
acid.  The  cathodes  consist  of  very  thin  sheets  of  pure  gold. 
To  insure  a  well  adherent  cathode-deposit,  the  temperature 
is  kept  at  about  70°  C.;  the  electrolyte  contains  3%  of  gold 
and  from  3%  to  4%  of  hydrochloric  acid.  The  voltage  em- 
ployed is  about  1  volt,  the  ND100  =  10  amperes.  The  pro- 
duct secured  contains  from  99.80%  to  100%  of  gold.  <| 

Lead.  —  While  there  seems  to  be  little  opportunity  for  a 
commercially  profitable  process  of  winning  crude  lead  elec- 
trolytically from  its  ores,  the  process  of  refining  crude  lead 
electrolytically  is  well  established,  one  of  the  chief  advan- 


100  NOTES  ON  ELECTROCHEMISTRY. 

tages  of  such  a  process  being  that  it  permits  the  obtainment 
of  a  pure  lead  and  of  a  pure  bismuth,  the  latter  a  common 
impurity  in  lead  won  by  metallurgical  processes. 

In  the  process  of  A.  G.  Betts,  lead  is  obtained  electroly- 
tically  by  dissolving  the  metal  in  hydrofluosilicic  acid,  which 
gives  an  electrolyte  of  lead-silicofluoride  from  which  metallic 
lead  is  deposited  at  the  cathode  in  the  form  of  a  dense  and 
smooth  deposit.  Addition  of  a  trace  of  gelatine,  an  organic 
colloid,  to  the  electrolyte  insures  the  coming  down  of  the 
electrolytic  deposit  in  a  finely  crystalline  condition.  The 
solution  is  kept  continuously  circulating  through  the  vats. 

The  anodes  are  crude  lead,  and  are  apt  to  contain  as  impur- 
ities some  copper,  antimony,  bismuth,  and  silver;  these  tend 
to  remain  in  the  anode-slime  provided  the  ND100  does  not 
exceed  1.0  ampere.  If  iron,  nickel,  and  zinc  are  also  present 
these  pass  into  the  solution.  The  voltage  employed  is  about 
0.4;  the  electrolyte  is  not  heated.  Starting  from  a  crude 
lead  containing  about  95%  of  the  metal,  the  refined  product 
is  practically  chemically  pure. 

Nickel. — The  application  of  electrical  energy  to  the  winning 
of  nickel  is  practically  confined  to  the  refining  of  this  metal. 

The  conditions  to  be  observed  in  order  to  deposit  nickel 
successfully  from  an  aqueous  solution  of  its  sulphate  or  its 
chloride  are  a  temperature  of  between  60°  and  70°  C.,  an  elec- 
trolyte containing  about  3%  of  nickel  together  with  a  trace 
of  free  sulphuric  acid  or  hydrochloric  acid,  a  normal  current 
density  of  from  0.5  to  2.5  and  a  voltage  of  from  1  to  2  volts. 
Generally  speaking,  the  higher  the  current  density  the  smoother 
and  the  brighter  the  deposit  secured. 

Electrodeposition  of  nickel  from  nickel  solutions  by  means 
of  insoluble  anodes  is  thoroughly  practicable.  Anodes  of 
lead-peroxide  have  been  used  for  the  purpose;  when  a  sul- 
phate salt  of  nickel  is  used  as  the  electrolyte,  the  sulphuric 
acid  set  free  in  the  operation  must  be  neutralized  with  nickel- 
hydrate  or  nickel-carbonate. 


ELECTROTECHNOLOGY.  101 

The  D.  H.  Browne  process,  formerly  used  by  the  Canadian 
Copper  Company,  was  worked  on  an  alloy  of  nickel  and 
copper,  containing  about  43%  of  the  former  and  54%  of  the 
latter  metal. 

This  alloy  was  cast  for  anodes;  some  of  it  was  also  used  as 
the  electrolyte,  being  treated  with  chlorine  and  sodium 
chloride,  which  brought  these  metals  into  solution  as  cuprous 
chloride  and  as  nickel  chloride.  Most  of  the  copper  having 
been  precipitated  from  this  solution  by  electrolysis,  the 
remainder  was  thrown  down  by  the  action  of  sodium  sul- 
phide, while  any  iron  and  cobalt  present  were  precipitated  by 
sodium  hydrate  and  by  chlorine. 

The  solution  thus  obtained  contained  practically  only  nickel 
chloride  and  sodium  chloride ;  the  latter  was  removed  by  con- 
centration and  crystallization  and  the  nickel  was  finally  pre- 
cipitated electrolytically  from  a  hot  solution.  The  voltage 
employed  for  this  purpose  was  about  3.5  volts;  the  anodes 
used  in  this  operation  were  made  of  graphite,  suspended  in 
vessels  of  porous  earthenware.  The  electrolyte  after  coursing 
through  the  vats  returned  to  the  evaporators,  where  it  suffered 
further  concentration.  The  chlorine  evolved  at  the  anodes 
was  made  to  dissolve  the  copper-nickel  alloy  used  as  elec- 
trolyte. The  nickel  won  by  this  process  attained  to  a  purity 
of  99.85%. 

Tin.  —  There  is  no  electrolytic  method  in  use  for  winning 
tin  from  its  ores,  or  for  refining  it,  however,  the  securing  of 
tin  from  tin-plate  scrap  is  quite  an  industry. 

Tin  plate  is  sheet  iron  coated  with  tin,  and  although  only 
a  thin  coating  of  this  metal  is  used  for  the  purpose,  a  large 
amount  of  tin  is  consumed  in  this  way.  The  scrap  from 
which  the  tin  is  thus  recovered  is  in  part  the  waste  of  new 
tin  plate  and  in  part  the  scrap  of  old  tinned  articles. 

Several  processes  have  been  devised  for  the  recovery  of 
tin  from  this  material.  Thus  Siemens  and  Halske  employ 
the  scrap  as  anode,  suspending  the  same  in  wooden  or  wicker 


102  NOTES  ON  ELECTROCHEMISTRY. 

baskets;  as  cathodes  they  employ  copper  which  has  been 
tinned.  In  the  process  chiefly  developed  by  the  Gold- 
schmidts  in  Essen,  Germany,  the  tin-plate  scrap,  containing 
about  30%  of  tin,  is  placed  in  iron  wire  baskets  which  are 
suspended,  as  anodes,  in  iron  vats.  The  latter  are  made  to 
serve  as  cathodes,  the  electrolyte  is  a  10%  solution  of  caustic 
soda.  The  operation  is  conducted  at  a  temperature  of  about 
70°  C.,  the  voltage  employed  is  1.5  volts.  In  the  tin  thus 
electrolytically  deposited,  lead  and  iron  are  apt  to  occur  as 
impurities.  The  iron  from  which  the  tin  coating  is  originally 
removed  is  fairly  pure  and  can  be  reworked. 

Tin  might  also  be  recovered  from  lead  scrap,  that  is  to  say, 
from  sheet  lead  or  from  pipes  upon  which  a  layer  of  tin  has 
been  rolled;  this  lead  scrap  could  be  made  the  anode,  and 
sulphuric  acid  might  be  employed  as  the  electrolyte.  In  such 
a  process  of  course  the  metallic  lead  would  remain,  barring 
a  small  percentage  of  the  metal  which  would  be  transformed 
into  sulphate,  while  the  tin  was  recovered. 

Zinc.  —  Electrolytic  processes  are  of  great  value  in  the 
obtainment  of  zinc  from  its  ores. 

In  Silesia,  Germany,  during  the  last  decade  of  the  past 
century,  a  process  was  in  use  wherein  zinc  sulphate  was  used 
as  the  electrolyte,  the  anodes  employed  being  made  of  lead 
peroxide;  it  was,  however,  ultimately  abandoned  because  it 
could  not  compete  commercially  with  other  metallurgical 
processes.  Among  more  recent  methods  of  winning  zinc 
electrolytically  from  its  ores,  must  be  named  the  Siemens- 
Halske  process,  the  Ashcroft  process,  and  the  Hoepfner  pro- 
cesses. 

In  the  Siemens-Halske  process,  as  well  as  in  that  of  Ash- 
croft,  the  ores  worked  are  essentially  compounds  of  lead 
sulphide  and  of  zinc  sulphide,  containing  approximately 
20%  of  zinc  and  30%  of  lead;  the  ores  are  also  argentiferous. 
In  one  of  the  processes  by  Hoepfner  the  crude  material 
worked  was  essentially  an  iron  ore  containing  about  10%  of 


ELECTRO  TECHNOLOG  Y.  103 

zinc;  the  electrolyte  used  was  a  solution  of  zinc  chloride, 
the  anodes  were  made  of  carbon,  the  cathodes  consisted  of 
revolving  zinc  plates  and  the  anode  and  cathode-chambers 
were  separated  by  diaphragms.  The  ND100  was  4  amperes, 
the  voltage  ranged  between  3  and  7  volts. 

In  another  Hoepfner  process,  used  in  England,  the  zinc  was 
roasted,  secured  as  an  oxide,  and  then  treated  with  a  hot 
concentrated  solution  of  magnesium  chloride  in  which  the 
oxide  of  zinc  dissolves  as  a  basic  salt.  This  solution  received 
subsequent  treatment  with  carbonic  acid  gas  and  with  cal- 
cium chloride  solution,  the  zinc  appearing  ultimately  as  zinc 
chloride,  which  solution  was  submitted  to  electrolysis.  Car- 
bon anodes  were  used,  the  ND100  =  1  ampere  and  the  voltage 
about  3  volts;  the  purity  of  the  resulting  product  was  99.95%. 

A  process  for  refining  zinc  electrolytically  has  been  devised 
by  Roessler  and  Edelmann.  In  this  method  the  crude  zinc, 
used  for  anodes,  contains  about  20%  of  impurities,  among 
which  should  be  noted  copper,  silver,  lead,  nickel,  and  cobalt. 
The  ND100  =  0.8  to  0.9  ampere,  the  voltage  ranges  from  1.25 
to  1.50,  the  electrolyte  is  not  heated.  From  the  anode-slime, 
silver,  copper,  and  lead  are  recovered  by  separate  processes. 
In  this  process  also  the  purity  of  the  refined  product  is  ap- 
proximately 99.95%. 

Electroplating. 

Electroplating.  —  The  first  electrotechnical  process  de- 
vised seems  to  have  been  the  electrodeposition  of  metals, 
the  art  of  electrotyping.  The  making  of  exact  metallic 
reproductions,  replicas,  of  objects  was  discovered  indepen- 
dently by  Jacobi,  by  Spencer,  and  by  Jordan;  the  first-named 
of  these  exhibited  electrotype  copies  of  medals  before  the 
Academy  of  St.  Petersburg  in  1838.  Two  years  later,  Murray 
discovered  that  non-conducting  bodies  when  coated  with 
graphite  would  serve  equally  well  as  a  base  for  electrodeposi- 


104  NOTES  ON  ELECTROCHEMISTRY. 

tion.     From  this  process  of  electrotyping,  a  few  years  later, 
the  process  of  electroplating  was  evolved. 

The  fundamental  difference  between  the  two  processes  is 
that  in  electrotyping  the  electrolytic  deposit  is  meant  to  be 
removed  from  the  surface  on  which  it  has  been  formed,  and 
therefore  too  firm  an  adherence  of  the  deposit  on  the  object 
on  which  it  is  made  must  be  avoided;  this  is  effected  by  giving 
to  the  object  a  preliminary  thin  coating  of  oil  or  of  a  solution 
of  some  salt.  In  electroplating  the  deposit  is  meant  to  ad- 
here as  firmly  to  the  object  as  if  it  had  been  welded  on  the 
same;  for  a  successful  electroplating  absolutely  clean  sur- 
faces are  therefore  an  essential  condition. 

While  for  a  long  time  it  has  been  known  that  the  chemical 
composition,  the  concentration,  and  the  temperature  of  the 
electrolyte,  as  well  as  the  current  density  employed,  are  all 
factors  of  importance  if  a  well-adherent  electrodeposit  is  to 
be  secured,  a  recent  study  of  the  subject  by  Wilder  D.  Ban- 
croft,* "  On  the  Chemistry  of  Electroplating,"  has  thrown  light 
on  many  aspects  of  the  problem  which  were  but  little  under- 
stood before. 

Among  other  interesting  facts  Bancroft  found  that  a  poor 
metallic  deposit  is  nearly  always  caused  by  the  precipitation 
of  some  salt  of  the  metal  in  place  of  the  pure  metal,  for  in- 
stance, by  the  formation  of  an  oxide,  a  hydro-oxide,  or  a  cyan- 
ide. Therefore,  the  addition  of  any  chemical  which  will 
dissolve  a  salt  or  which  will  prevent  its  formation  must  im- 
prove the  quality  of  the  desired  electrodeposit. 

Maintenance  of  proper  temperature  conditions  is  likewise 
essential,  as  is  also  the  rate  at  which  the  electrolyte  is  stirred, 
for  a  sufficiently  concentrated  solution  must  always  be  main- 
tained at  the  cathode;  too  dilute  a  solution  at  the  cathode 
results  in  the  formation  of  sandy  or  pulverulent  deposits. 

Determining   the   best   conditions   in   individual   cases   re- 
quires considerable  care  and  experimenting,  yet  the  general 
*  Journal  of  the  Franklin  Institute,  1905,  Vol.  140,  p.  139. 


ELECTROTECHNOLOGY.  105 

principles  underlying  electroplating  are  very  simple.  The 
object  to  be  plated  is  put  into  an  electrolyte  which  is  a  solu- 
tion of  some  salt  of  the  metal  with  which  the  plating  is  to  be 
done.  This  solution  is  termed  the  bath.  The  object  to  be 
plated  is  attached  to  a  wire  leading  in  from  the  zinc  plate  of 
a  primary  battery,  or  from  the  negative  pole  of  a  dynamo; 
in  short,  the  object  to  be  plated  is  made  the  cathode  of  the 
bath.  The  metal  with  which  the  object  is  to  be  plated  is  sus- 
pended in  the  bath  from  another  wire  which  comes  from  the 
carbon,  or  copper  electrode  of  the  primary  battery,  or  from 
the  corresponding  pole  of  the  dynamo.  The  metal  which  is 
thus  to  be  deposited  on  the  object  is  termed  the  anode  of  the 
bath. 

In  general  it  may  be  said  that  the  working  conditions  for 
electroplating  are  a  low  voltage  and  a  fairly  strong  current. 
The  voltages  employed  range  between  1  and  5  volts,  the  cur- 
rent densities  of  course  differ  considerably  for  the  different 
metals;  some  ND100  values  are: 


For  gilding,  0.2  ampere, 

For  silvering,  0.3  to  0.6  ampere. 

For  nickeling,  0.3  to  0.6  amperes, 

For  copper  plating,  0.4  ampere, 

For  zinc  plating,  1.0  to  3.0  amperes. 


A  careful  study  of  the  conditions  necessary  to  secure  a  good 
and  well  adherent  electrodeposit  of  zinc  has  been  made  by 
Mylius  and  Fromm.*  From  this  it  appears  that  the  best 
working  conditions  —  when  zinc  sulphate  is  employed  as  the 
electrolyte  —  are  to  have  4  to  6%  of  zinc  in  the  electrolyte, 
a  ND100  =  1  to  3  amperes,  and  a  voltage  of  from  3  to  4  volts. 
Above  all,  it  is  necessary  to  suppress  as  far  as  possible  the 
liberation  of  free  hydrogen  at  the  cathode,  for  this  causes  a 
basic  condition  in  the  electrolyte  near  the  cathode,  a  condi- 
tion conductive  to  the  deposition  of  spongy  zinc  and  inter- 
*  Zeitschrift  f.  Anorg:  Chemie,  1895,  p.  144. 


106  NOTES  ON  ELECTROCHEMISTRY. 

fering  with  the  precipitation  of  a  firm,  coherent  deposit  of  the 
metal.  The  presence  of  mere  traces  of  some  other  metals 
more  electronegative  than  zinc,  also  tends  to  the  formation 
of  spongy  zinc,  and  such  metals  should  therefore  be  removed 
before  electrolysis. 

Alloys  also  can  be  deposited  by  electroplating;  thus  it  is 
possible  to  make  an  electroplate  of  brass  by  using  a  solution 
of  cyanide  of  zinc  and  of  cyanide  of  copper,  both  dissolved 
in  potassium  cyanide.  Bronzes,  that  is  to  say,  alloys  of 
copper  and  tin,  can  also  be  electroplated,  the  deposition 
taking  place  from  mixed  solutions  of  their  salts.  Thus  far, 
however,  alloys  have  not  been  extensively  used  in  electro- 
plating. 

Chlorine  and  Alkali- Hydrates. 

Chlorine  and  Alkali-Hydrates.  —  In  the  electrolytic  win- 
ning of  chlorine  and  of  alkali-hydrates  from  solutions  of 
alkaline  chlorides,  the  fundamental  principle  to  be  observed 
is  the  keeping  separate  of  the  products  produced  at  the 
cathode  from  those  produced  at  the  anode.  At  the  cathode, 
alkali  and  hydrogen  are  generated,  at  the  anode,  of  course, 
chlorine. 

To  achieve  this  holding  apart  of  the  products  of  the  reaction, 
three  different  kinds  of  processes  have  been  devised;  these 
may  be  designated  respectively  as: 

I.    The  diaphragm  process. 
II.    The  bell  process. 
III.    The  mercury  process. 

The  chlorine  gas  which  is  obtained  by  these  processes  is 
either  liquefied  and  thus  made  available  for  shipment,  or  it 
is  transformed  into  bleaching  powder;  the  alkali  obtained 
can,  of  course,  be  readily  turned  into  the  caustic  condition. 
Probably  the  chief  reason  why  the  entire  output  of  caustic 
alkali  needed  in  the  chemical  industry  is  not  produced  exclu- 


ELECTROTECHNOLOGY.  107 

sively  by  electrolytic  methods,  for  these  methods  are  eco- 
nomical, is  the  fact  that  there  is  not  a  sufficiently  large 
demand  for  the  chlorine  which,  of  course,  is  simultaneously 
produced  in  quantity  equivalent  to  the  alkali  obtained. 

The  hydrogen  gas  which  is  incidentally  produced  with  the 
alkali  is  in  many  factories  allowed  to  escape  unused;  in  some 
places  it  is  employed  in  the  manufacture  of  fuel-gas,  and  in 
others  it  is  condensed  under  pressure  and  is  thus  made  avail- 
able for  transportation. 

The  crude  chemicals  employed  in  the  electrolysis  of  alkali- 
chlorides  are  essentially  chloride  of  potassium,  obtained  from 
<jarnallite  and  common  salt.  It  is  very  important  that 
only  pure  solutions  of  the  alkali-chlorides  be  used  for  elec- 
trolysis, for  appreciable  amounts  of  impurities  interfere 
seriously  with  the  working  of  the  processes  and  with  the 
quality  of  the  products  obtained. 

In  cases  where  the  products  liberated  at  the  two  electrodes 
are  not  kept  separate,  and  where  a  free  intermixing  of  the 
cathode  and  anode-solutions  is  allowed,  hypochlorites  and 
chlorates  will  be  formed,  according  to  the  temperature  and 
the  current  density  employed. 

The  former  salts,  that  is  to  say,  the  hypochlorites,  are  pro- 
duced at  the  anode  when  a  low  temperature  and  a  low  current 
density  are  used;  such  hypochlorite  solutions,  practically  not 
exceeding  2  or  3%  in  strength,  are  best  used  on  the  spot  for 
electrolytic  bleaching.  The  formation  of  chlorates  is,  on  the 
other  hand,  favored  by  the  use  of  a  high  current  density  and 
the  presence  of  some  alkali.  Thus,  potassium  chlorate  is  now 
made  almost  exclusively  by  electrolysis,  about  5  kilowatt- 
hours  being  used  per  kilogram  of  potassium  chlorate  pro- 
duced. If  this  product  is  subjected  to  further  electrolytic 
treatment  with  a  high  current  density,  at  a  low  temperature, 
potassium  per-chlorate  results. 

I.  Diaphragm  Process.  —  The  principal  problem  to  be 
solved  in  processes  of  this  description,  is  to  find  a  suitable 


108  NOTES  ON  ELECTROCHEMISTRY. 

material  which  shall  prove  resistant  alike  to  chlorine  and  to 
alkali.  In  Germany,  after  a  great  deal  of  experimenting, 
plates  of  Portland  cement  were  selected  for  the  purpose: 
in  the  United  States,  asbestos  is  the  material  generally 
used. 

From  the  very  fact  that  any  material  serviceable  for 
diaphragms  must  be  sufficiently  porous  to  permit  of  the 
passing  of  the  electric  current,  it  is  unavoidable  that  a  part 
of  the  hydroxyl  ions  set  free  will  also  pass  through,  and  these, 
naturally  leacting  with  some  of  the  chlorine  which  is  liberated, 
will  cut  down  the  output  of  that  gas. 

Carbon  anodes  are  preferably  employed,  the  working 
temperature  is  held  at  about  85°  C.,  the  ND100  ranges  from 
about  1  to  2  amperes  at  the  diaphragm.  In  some  processes 
the  alkali-chloride  solution  is  conducted  only  to  the  cathode 
compartment  (Griesheim-Electron  system),  in  others  the 
solution  of  the  electrolyte  flows  from  the  anode  compartment 
to  the  cathode  compartment  (Systems  of  McDonald,  and  of 
Hargreaves  and  Bird ) . 

II.  Bell  Process.  —  The  fundamental  principle  of  processes 
of  this  description  is  the  use  of  some  non-porous,  non-con- 
ducting medium,  which  serves  to  keep  separate  the  solutions 
at  the  anode  and  at  the  cathode,  while  it  permits  those  parts  of 
the  solution  not  in  contact  with  the  gases  set  free  at  the 
electrodes  to  intermingle  freely. 

The  bell  device  consists  essentially  of  a  vessel,  technically 
the  bell,  which  is  generally  an  open  box  made  of  sheet  iron 
and  coated  with  some  non-conducting  material.  This  bell 
is  suspended  with  the  open  side  downward  in  a  vat  or  chamber, 
likewise  constructed  of  some  non-conducting  material;  into 
this  chamber  the  electrolyte  is  placed.  A  perforated  carbon 
anode  is  hung  inside  of  the  bell  and  the  chlorine  generated  at 
this  anode  is  carried  away  by  an  exit- tube  which  passes 
through  the  upper  part  of  the  bell.  The  cathode  is  placed  in 
the  outer  vessel  and  the  alkaline  lye  which  is  generated  at  the 


ELECTLOTECHNOLOGY.  109 

• 
cathode  passes  off  through  an  overflow  placed  at  the  top  of 

the  vat. 

Generally  a  number  of  such  bells  are  linked  together  in 
parallel;  the  total  number  of  bells  employed  in  a  plant,  in 
some  works,  runs  up  to  twenty  or  thirty  thousand.  Details 
as  to  the  current  density  and  other  working  conditions  are 
not  publicly  known,  but  Foerster*  infers  that  the  ND100  ranges 
from  2  to  4  amperes,  that  the  temperature  does  not  exceed 
30°  or  35°  C.,  and  that  the  voltage  used  is  about  4  or  5  volts. 

III.  The  Mercury  Process.  —  The  essential  feature  of  the 
processes  using  mercury  as  the  cathode  is  the  formation  of  an 
amalgam  of  the  alkali  metal  liberated  by  electrolysis. 

In  Castner's  process  —  the  Castner  Electrolytic  Alkali  Com- 
pany was  the  first  to  manufacture  chlorine  and  caustic  soda 
—  the  production  and  the  decomposition  of  this  amalgam  are 
carried  out  in  the  same  apparatus.  A  box  is  divided  into 
three  compartments  by  the  use  of  partitions  which  reach 
almost,  but  not  quite,  to  the  base  of  the  box;  this  base  is 
covered  with  a  layer  of  mercury.  The  two  outside  compart- 
ments are  closed  on  top  and  suspended  in  them  are  the  car- 
bon anodes  which  reach  down  almost  to  the  mercury. 

The  electrolyte  employed  is  a  solution  of  sodium  chloride, 
which  suffers  electrolysis  in  the  outer  chambers.  The  central 
chamber,  which  contains  an  iron  electrode  in  a  weakly  alka- 
line solution,  serves  for  the  decomposition  of  the  amalgam 
into  mercury  and  sodium-hydrate.  The  whole  apparatus  is 
so  arranged  that  it  can  be  given  a  rocking  motion  and  during 
the  operation  it  is  kept  constantly  moving. 

The  electric  current  is  obliged  to  pass  from  the  anodes  by 
way  of  the  mercury  to  the  cathode  which  is  situated,  as  will 
be  recalled,  in  the  central  compartment.  The  mercury,  act- 
ing as  cathode  in  the  two  outer  chambers,  amalgamates  with 
the  sodium  and  then  gives  up  this  alkali  in  the  cathode 
chamber,  where  the  mercury  acts  as  anode,  the  alkali  dissolv- 
*  Liber,  cit.  p.  417. 


110  NOTES  ON  ELECTROCHEMISTRY. 

• 

ing  in  the  water  and  the  hydrogen  gas  escaping.     The  ND10() 

at  the  cathodic  mercury  is  about  7  amperes,  at  the  anodic 
mercury,  about  12  amperes;  the  voltage  is  about  4  volts. 
The  product  obtained  by  the  Castner  process  is  very  pure. 
The  chlorine  is  generally  turned  into  chloride  of  lime. 

A  process  differing  from  but  planned  on  lines  similar  to 
those  just  referred  to,  is  Kellner's  process,  and  in  England 
the  Castner- Kellner  Company  makes  use  of  a  method  embody- 
ing the  fundamental  principles  of  both  of  these  systems. 

A.  II.    INDIRECT  ACTION  PROCESSES. 
Electrodeposition  from  Fused  Electrolytes. 

Introduction.  —  In  electrolytic  processes  where  the  prod- 
uct is  obtained  from  a  fused  electrolyte,  the  electrical  energy 
is  in  part  used  for  the  actual  electrolytic  work  and  in  part  for 
the  fusing  of  the  electrolyte. 

The  relation  between  electrical  energy  and  heat  energy  is 
expressed  by  Joule's  law  (1841):  "  the  heat  developed  in  a 
conductor  is  proportional  to  the  resistance  encountered  and 
to  the  square  of  the  strength  of  the  current." 

If:  resistance  =  R 

current  strength  =  C 
heat  =  H 

then,  H  =  C2  R  0.24. 

The  heat  thus  generated  electrically,  not  chemically,  is 
termed  Joule's  heat. 

To  illustrate,  assume: 

Resistance  equal  to  2  ohms. 

Current  strength  equal  to  50  amperes. 

Then,  50  X  50  X  2  x  1  =  6000  joules  per  second. 

As  one  joule  equals  0.00024  large  Calorie,  or  0.24  small 
calorie,  5000  joules  =  5000  X  0.00024  =  1.200  Calories  or, 
5000  X  0.24  =  1200  calories. 


ELECT  ROT  EC  HXOLOG  Y.  Ill 

In  passing  through  a  circuit  embracing  an  electrolyte, 
Joule's  heat  is  generated  in  all  parts  of  the  circuit  in  amounts 
proportionate  to  the  resistance  of  the  respective  parts  of  the 
circuit  and  to  the  square  of  the  current. 

The  actual  temperature  to  which  an  electrolyte  thus  attains 
in  a  given  time  under  given  conditions  of  current  strength 
and  resistance  depends  upon  its  mass,  its  specific  heat,  and 
upon  the  success  with  which  loss  of  heat  by  radiation,  and 
by  other  causes,  can  be  avoided. 

An  important  point  to  be  borne  in  mind  in  attempting  to 
secure  a  metal  from  a  fused  electrolyte  is  that  the  boiling 
point  of  the  metal  must  not  lie  too  close  to  the  point  of  fusion 
of  the  electrolyte,  otherwise  volatilization  of  the  metal  would 
almost  keep  pace  with  its  electrolytic  production. 

The  metals  whose  production  from  a  state  of  fusion  shall 
now  be  briefly  considered  are  aluminium,  magnesium,  and 
sodium. 

Aluminium.  —  Various  processes  have  been  devised  for 
the  electrolytic  winning  of  aluminium.  The  methods,  how- 
ever, principally  employed  are  the  Heroult  process  and  the 
Hall  process.  Chemically,  these  two  processes  are  very  much 
alike,  in  both,  pure  alumina  (A12O3)  is  added  to  the  fused 
double  fluoride  of  aluminium  and  sodium,  A12F6,  6  NaF,  a 
mineral  called  cryolite. 

In  putting  the  process  into  operation  the  cryolite  is  first 
brought  into  a  state  of  fusion  in  iron  furnaces  and  then  the 
anodes  are  lowered  into  it  and  electrolysis  commences.  As 
the  aluminium  separates  at  the  cathode,  alumina  is  fed  into 
the  bath  so  as  to  keep  the  amount  of  aluminium  present  in 
the  electrolyte  about  constant.  The  metal  being  specifically 
heavier  than  the  fused  electrolyte,  sinks  to  the  bottom  of  the 
fusion  chamber,  whence  it  is  tapped,  generally  once  a  day. 
The  anodes  are  made  of  carbon,  the  cathodes  are  generally 
made  of  iron,  but  these  also  can  be  made  of  carbon. 

In  the  Hall  process,  the  amperage  used  per  fusion  chamber1: 


112  NOTES  ON   ELECTROCHEMISTRY. 

is  about  10,000  amperes,  the  voltage  employed,  about  5  volts. 
The  temperature  of  the  bath  is  held  in  the  neighborhood  of 
1000°  C.,  being  kept  as  low  as  possible.  The  fusion  chambers 
are  discharged  at  stated  intervals. 

In  the  Heroult  process,  about  8000  amperes  per  furnace  are 
required,  the  voltage  ranges  from  3  to  5  volts,  the  ND100  =  190 
amperes  and  the  temperature  is  held  between  750°  and  850°  C. 

The  chemical  reactions  taking  place  during  electrolysis 
consist  in  the  liberation  of  aluminium  at  the  cathode  and  of 
oxygen  at  the  anode;  this  oxygen  of  course  combines  with  the 
carbon  anodes  to  form  carbon  monoxide.  The  pure  alumina 
which  is  used  in  the  process  is  generally  obtained  from  the 
mineral  bauxite,  which  is  passed  through  a  preliminary  puri- 
fying operation  by  roasting  and  by  subsequent  treatment 
with  caustic  soda,  or,  according  to  a  recent  process  devised 
by  C.  M.  Hall,  bauxite  as  well  as  other  impure  aluminium 
oxides  are  purified  by  fusion  with  the  electric  current,  the 
impurities  present  being  reduced  in  the  fused  bath. 

Estimates  vary  as  to  the  amount  of  electrical  energy  nec- 
essary in  the  Hall  process,  for  the  production  of  one  kilogram 
of  aluminium.  Bucherer  places  it  at  32.7,  Becker  at  30,  and 
J.  W.  Richards  at  22  kilowatt-hours. 

Of  the  total  electrical  energy  consumed  in  the  production 
of  aluminium,  it  is  calculated  that  about  four-fifths  are  used 
for  the  heating  and  the  balance  for  the  actual  electrolytic 
work.  The  electrical  energy,  which  is  expended  in  effecting 
the  separation  of  metallic  aluminium  from  its  chemical  com- 
binations, can  of  course  be  recovered  as  heat  energy  when  the 
metal  is  caused  to  re-combine  with  oxygen;  this  is  the  case, 
for  instance,  in  the  Thermite  process. 

According  to  the  report  of  the  United  States  Geological 
Survey,  the  world's  production  of  aluminium  in  1903  was 
over  eighteen  million  pounds,  of  which  seven  and  a  half 
millions  were  produced  in  the  United  States,  the  balance  being 
made  in  Switzerland,  France,  and  Great  Britain. 


ELECTRO  TECHNOLOG  Y.  113 

In  1904  production  of  this  metal  in  the  United  States, 
which  in  1883  had  amounted  to  only  83  pounds,  was  8,600,000 
pounds.  The  sole  'producer  in  the  United  States  is  the 
Pittsburg  Reduction  Company,  which  at  present  has  five 
plants  in  operation. 

The  purity  of  commercial  aluminium  is  about  99%,  the 
impurities  constituting  the  balance  are  principally  iron, 
copper,  silicon,  and  carbon. 

Magnesium.  —  The  raw  material  from  which  magnesium  is 
won  electrolytically  is  carnallite,  a  double  chloride  of  potas- 
sium and  magnesium,  which  is  carefully  dehydrated  before 
fusion;  its  fusion  temperature  is  be  ow  700°  C. 

As  in  this  process  the  product  liberated  at  the  anode  is 
chlorine,  the  apparatus  must  of  course  be  arranged  so  as  to 
prevent  this  gas  from  combining  with  the  magnesium  which 
is  set  free  at  the  cathode.  In  one  form  of  apparatus  this  is 
accomplished  by  conducting  the  electrolysis  in  a  steel  vat, 
the  walls  of  which  serve  as  cathodes;  in  the  center  of  this  vat 
there  is  introduced  the  carbon  anode,  inclosed  in  a  porcelain 
cylinder,  which  is  provided  with  a  tube  from  which  the  chlo- 
rine gas  escapes. 

The  ND100  used  is  from  11  to  15  amperes,  the  voltage  is 
about  4  volts.  Care  is  taken  to  have  the  electrodeposition 
of  the  magnesium  take  place  in  an  inert  atmosphere;  for  this 
purpose  either  nitrogen,  or  some  gaseous  mixture  devoid  of 
free  oxygen,  is  introduced  into  the  cathode  compartment. 

Sodium.  —  The  most  important  process  for  making  sodium 
electrolytically  from  caustic  soda  is  Castner's  process.  The 
products  of  the  electrolysis  are  sodium,  hydrogen,  and  oxy- 
gen. The  anodes  are  made  of  nickel,  of  iron,  or  of  steel,  and 
are  annular  or  cylindrical  in  shape. 

The  cathode,  generally  made  of  nickel,  projects  upward 
into  a  collecting  chamber  and  into  a  cylinder  of  wire  gauze  in 
which  the  metallic  sodium  accumulates,  and  which  hinders  it 
from  passing  into  the  anode-chamber;  the  hydrogen  gas  in 


114  NOTES  ON  ELECTROCHEMISTRY. 

the  cathode  chamber  prevents  the  oxidation  of  the  sodium. 
The  temperature  is  carefully  held  between  310°  and  330°  C. 
The  voltage  used  is  about  5  volts,  and  each  furnace  uses  about 
1200  amperes. 

A  recent  process,  devised  by  E.  A.  Ashcroft,  consists  of  a 
cell  wherein  fused  sodium  chloride,  the  electrolyte,  rests  on 
fused  lead,  which  acts  as  cathode;  the  anode  is  made  of 
carbon  and  the  chlorine  is  there  liberated.  The  sodium 
alloys  with  the  fused  lead,  and  this  alloy  is  conveyed  to  an 
outside  compartment  where  it  acts  as  the  anode,  the  cathodes 
being  either  iron  or  nickel,  and  the  electrolyte  consisting  of 
fused  sodium  hydrate.  In  this  outer  chamber  metallic 
sodium  is  set  free  at  the  cathode. 

A  process  devised  by  Acker  Bros.,  makes  use  of  fused 
sodium  chloride  as  the  electrolyte,  the  same  being  well  dried 
before  fusion.  The  anodes  consist  of  graphite,  and  fused  lead 
serves  as  cathode,  as  in  the  Ashcroft  process. 

The  lead-sodium  alloy  is  decomposed  at  red  heat  by  steam 
blown  in  under  pressure,  the  resultant  products  are  molten 
lead,  sodium  hydrate,  and  hydrogen  gas.  The  voltage 
employed  is  about  7  volts,  the  ND100  about  290  amperes,  each 
furnace  taking  8000  amperes;  a  part  of  this  energy  is  used 
to  keep  the  sodium  chloride  in  a  state  of  fusion  without 
application  of  heat  from  any  outside  source.  The  chlorine 
evolved  was  formerly  turned  exclusively  into  chloride  of  lime, 
but  recently  the  Acker  Process  Company  have  devised  new 
uses  for  the  chlorine,  and  among  other  products  now  manu- 
facture tetrachloride  of  carbon  and  tetrachloride  of  tin. 

Electr other mic  Processes. 

Electro-furnaces.  —  In  conductors  of  the  first  class,  that  is 
to  say,  in  all  metals  and  in  carbon,  all  electrical  energy  can 
be  converted  into  heat  energy. 

The  formula  by  means  of  which  the  heat  equivalent,  in 
calories,  of  a  given  amount  of  electrical  energy  can  be  figured 


ELECTROTECHNOLOGY.  115 

is,  it  will  be  recalled,  very  simple.  Designating  the  heat 
equivalent  by  H,  the  resistance  by  R,  the  current  strength 
by  C,  the  result  desired,  expressed  in  gram  calories,  is: 

H  =  C2R  0.24 

Probably  the  first  one  to  suggest  the  application  of  electri- 
cal energy  for  electrothermic  work  on  a  commercial  scale, 
was  Sir  William  Siemens,  in  1880. 

The  transformation  of  electrical  energy  into  heat  energy  is, 
in  practice,  accomplished  in  several  ways,  and  at  least  four 
types  of  electrical  furnaces  may  be  distinguished: 

1.  The  arc  furnace. 

2.  The  resistance,  or  incandescent  furnace. 

3.  The  transformer,  or  induction  furnace. 

4.  The  tube  furnace. 

Arc  furnaces  may  be  divided  into  two  groups,  direct  and 
indirect  arc  furnaces.  In  the  former,  the  material  to  be  sub- 
jected to  the  influence  of  the  heat  generated  by  the  trans- 
formation of  electrical  energy,  is  exposed  directly  to  the 
electric  arc;  in  the  indirect  type  the  material  to  be  treated  is 
not  exposed  to  the  direct  action  of  the  arc  but  receives  its 
heat  indirectly,  the  heat  being  reflected  from  the  interior  of 
the  chamber  in  which  the  reaction  takes  place  and  into  which 
the  electrodes  project. 

Of  course  the  forms  which  may  be  given  to  arc  furnaces  are 
varied,  but  the  principal  feature  embodied  in  all  furnaces  of 
this  description  is  a  hearth  constructed  of  some  fire-resisting 
material,  fire-brick  or  the  like,  and  carbon  electrodes,  which 
project  into  this  fusion  chamber.  The  current  is  supplied  by 
means  of  heavy  cables  clamped  to  these  carbon  electrodes. 

As  before  stated,  the  material  to  be  acted  on  may  be  either 
exposed  to  the  direct  heat  of  the  arc,  or  else  it  may  be  so 
placed  that  it  receives  only  radiated  and  reflected  heat  from 


116  NOTES  ON  ELECTROCHEMISTRY. 

the  walls  and  the  roof  of  the  furnace  chamber.  An  illustra- 
tion of  the  former  type  is  offered  by  the  aluminium  furnace 
during  the  time  when  the  cryolite  and  the  alumina  are  being 
fused,  that  is  to  say,  before  electrolysis  proper  has  begun. 
As  an  illustration  of  the  indirect  action  type  of  arc  furnace, 
there  may  be  mentioned  the  furnace  used  by  Moissan  in 
some  of  his  famous  researches,  and  the  De  Chalmont  furnace 
employed  for  the  reduction  of  metallic  silic.des,  for  in  these 
the  charge  is  also  exposed  only  to  the  radiated  heat  of  the  arc. 

Resistance,  or  incandescent  furnaces,  were  probably  first 
devised  by  E.  H.  Cowles  and  A.  H.  Cowles,  of  Cleveland, 
Ohio,  in  1885.  The  principle  upon  which  these  furnaces  are 
constructed  is  to  have  some  material  in  the  circu  t  of  the 
electric  current  which  will  offer  a  high  resistance  to  the 
passage  of  the  current,  in  consequence  of  which  high  temper- 
atures are  generated. 

Where  highest  temperatures  are  sought,  the  arc  furnace  is 
indicated,  but  where  closer  regulation  and  control  of  the 
working  temperatures  are  demanded,  resistance  furnaces 
offer  decided  advantages. 

The  degree  of  temperature  attained  in  the  resistance  fur- 
nace is  determined  by  the  magnitude  of  the  current,  the 
time  during  which  this  flows,  and  the  amount  of  resistance 
offered  by  the  circuit  through  which  the  current  passes. 

The  ultimate  temperature  attained  is  the  outcome  of  the 
rate  at  which  heat  is  generated  in  the  resistant  body  —  the 
core,  and  the  rate  at  which  this  heat  suffers  dissipation.  The 
point  at  which  these  two  conditions  counterbalance  each 
other  determines  the  highest  temperature  of  the  furnace. 

In  the  resistance  furnace,  the  material  to  be  heated  can 
itself  be  made  the  resistant  body,  or  the  latter  can  be  em- 
bodied as  a  core  in  the  material  to  be  treated.  In  such 
cases,  the  material  generally  employed  is  carbon,  coarsely 
grained. 

The    Acheson   furnaces   well    illustrate    that   type   of   the 


ELECROTECHNOLOGY.  117 

resistance  furnace  in  which  the  core  is,  in  part,  formed  by  the 
material  to  be  acted  upon. 

Borcher's  furnace  is  an  instance  of  the  other  type  of  resis- 
tance furnace,  that  is  to  say,  of  a  furnace  in  which  the  resis- 
tance core  is  independent  of  the  charge.  A  thin  pencil  of 
carbon  is  imbedded  in  the  mass  to  be  subjected  to  heating, 
and  a  powerful  electric  current  is  transmitted  to  this  car- 
bon pencil  by  carbon  bars  or  cylinders  very  much  greater 
in  diameter  than  the  pencil.  Naturally  an  intense  heat 
is  generated  at  the  pencil  owing  to  the  resistance  offered,  and 
as  carbon  does  not  volatilize  appreciably  below  3000°  C., 
very  high  temperatures  can  conveniently  be  obtained. 

In  transformer,  or  induction  furnaces,  of  which  Kjellin's 
furnace  for  steel  production  may  serve  as  a  type,  the  heat  is 
produced  by  induction,  the  current  in  the  furnace  being 
induced  by  an  alternating  current  passing  through  an  outside 
conductor  near  by,  generally  a  coil  of  many  turns  which 
incloses  the  furnace. 

Induction  furnaces  are  advantageously  used  for  smelting 
platinum;  in  Sweden  they  are  used  for  working  iron  ores  and, 
as  indicated  above,  for  the  production  of  a  special  grade  of 
steel. 

The  characteristic  feature  of  tube-furnaces  is  the  tubular 
form  of  the  hearth,  the  current  passing  through  and  heating 
the  walls  of  the  tube,  which  is  constructed  of  some  refrac- 
tory material. 

H.  Noel  Potter  has  devised  a  number  of  furnaces  of  this 
type  in  which  he  has  sought  to  secure  a  uniform  heating  of 
the  whole  tube,  satisfactory  terminal  connections,  and  a 
ready  replacement  of  the  worn  parts.  One  of  the  forms  he 
has  devised  consists  of  a  carbon  tube  supported  by  carbon 
rings  between  which  magnesia,  covered  by  asbestos,  is  packed, 
the  whole  being  inclosed  in  a  porcelain  tube. 

Another  of  Potter's  furnaces  consists  of  a  tube  made  from 
the  oxides  of  magnesia,  yttria,  and  zirconia  inclosed  in  a 


118  NOTES  ON  ELECTROCHEMISTRY. 

second  tube  made  of  one  of  these  oxides.  On  this  outer 
tube,  over  a  layer  of  mica,  a  coil  is  wound  in  which  electrical 
action  is  started;  the  actual  heating  effect,  however,  is  pro- 
duced in  the  interior  tube.  This  furnace  is  chiefly  used  for 
the  baking  of  Nernst  lamp  glowers. 

Among  other  tube  furnaces,  mention  should  be  made  of 
the  one  designed  by  A.  H.  Eddy,  used  for  the  application  of 
enamels,  and  that  of  Nernst  and  Glaser,  which  has  a  resistance- 
tube  made  of  electrolytic  oxides,  the  outer  tube  consisting  of 
loosely  packed  oxides  and  all  inclosed  in  a  jacket  designed 
to  prevent  loss  of  heat  by  radiation. 

A  very  convenient  electro-furnace  for  certain  laboratory 
purposes  is  used  by  the  Technische  Reichsanstalt  at  Char- 
lottenburg,  for  high  temperature  work.  It  is  made  of  several 
concentric  porcelain  tubes,  and  the  heating  is  effected  by 
passing  an  electric  current  through  wires  which  are  wound 
upon  some  of  these  tubes. 

Recently  an  electric  furnace  which  can  be  used  in  connec- 
tion with  a  vacuum,  and  for  general  analytical  purposes,  has 
been  devised  by  the  firm  of  Heraeus,  Germany.*  These 
furnaces  can  be  used  with  direct  current  at  a  potential  of 
from  65  to  220  volts,  and  require  only  from  1.5  to  2.5  amperes. 
The  uniformity  of  temperature,  which  can  be  maintained  in 
these  furnaces,  and  the  avoidance  of  reducing  gases,  which 
the  use  of  fuel  gas  often  entails,  are  valuable  features. 

In  some  electrothermic  furnaces  the  process  is  a  continu- 
ous one,  that  is  to  say,  the  process  is  not  interrupted  for  the 
introduction  of  charges,  nor  for  the  withdrawal  of  the  prod- 
uct. It  is,  however,  not  always  possible  to  arrange  a  working 
system  in  this  way,  and  therefore  many  furnaces  are  inter- 
mittent in  their  action. 

The  electric  furnace  undoubtedly  permits  the  securing  of 
a  higher  temperature  than  can  be  secured  through  any  other 
device.  Whereas  the  maximum  temperature  obtainable  by 
*  Chemiker  Zeitung,  1905,  Vol.  29,  p.  1209. 


ELECTROTECHNOLOGY.  119 

the  combustion  of  fuel  under  the  most  favorable  conditions 
is  probably  not  above  2000°  C.,  the  temperature  of  the  elec- 
tric arc  has  been  estimated  —  by  Violle  in  1893  —  at  about 
3600°  C.,  and  it  will  probably  be  reasonable  to  regard  this  as 
the  highest  temperature  maintainable  in  arc  furnaces  under 
ordinary  conditions.  In  furnaces  provided  with  additional 
protection  against  loss  of  heat  by  radiation,  for  instance,  in 
furnaces  having  an  additional  lining  of  some  good  non-con- 
ductor, like  magnesia  or  chalk,  temperatures  up  to  4000°  C. 
can  be  secured;  speaking,  however,  of  practical  electrical 
furnaces  working  on  a  commercial  scale,  the  working  tem- 
peratures of  these  will  range  from  about  2000  to  3500°  C. 

Where  no  electrochemical,  but  only  electrothermic  work 
has  to  be  done,  preference  is  given  to  the  alternating  rather 
than  to  the  direct  current. 

In  considering  the  cost  of  electric  furnaces,  the  cost  of  the 
electrical  energy  to  be  used  is  naturally  a  factor  of  the  great- 
est importance.  Where  such  energy  has  to  be  generated  by 
the  combustion  of  fuel,  the  cost  will  necessarily  be  high, 
because  only  a  small  percentage,  possibly  from  5  to  8%  of 
the  heating  power  of  the  coal  which  is  burned  under  the 
boiler,  is  actually  gained  in  the  form  of  electrical  energy. 
Where  water-power  is  available,  the  conditions  are  far  more 
favorable,  and  it  does  not  appear  improbable  that  in  the  near 
future  wind-power  may  be  made  to  serve  for  the  cheap  gen- 
eration of  electricity  for  electrothermic,  as  it  now  does  for 
other  purposes.* 

Electro-Furnace  Products.  —  A  number  of  substances  have 
been  prepared  by  the  aid  of  the  high  temperatures  made 
available  through  electro-furnaces.  Some  of  these  are  metals 
won  in  the  free  state  through  the  dissociation  of  their  com- 
pounds —  for  carbon  at  the  heat  of  the  electro-furnace  can 

*  Paul  la  Cour  (Aus  dem  Danischen  iibersezt  von  J.  Kaufmann): 
Die  Windkraft  und  ihre  Anwendung  zum  Antrieb  von  Elektrizitats- 
Werken,  Leipzig,  1905. 


120  NOTES   ON  ELECTROCHEMISTRY. 

remove  oxygen  from  any  metallic  oxide  known;  other  sub- 
stances produced  are  compounds,  the  chemical  union  of 
their  constituents  being  effected  by  the  aid  of  electrical 
energy. 

The  metallic  products  of  electro-furnaces  shall  be  first 
considered. 

Chromium.  —  This  metal  has  been  obtained  in  the  electric 
furnace  from  various  raw  materials.  If  a  mixture  of  chromic 
oxide  (Cr2O3)  and  carbon  are  fused,  carbides  of  chromium 
result,  and  from  these,  by  fusion  with  lime,  the  greater  portion 
of  carbon  can  be  removed.  The  metal  thus  produced  con- 
tains between  97%  and  98%  of  chromium,  and  carbon,  iron, 
and  silicon  as  impurities.  If  perfectly  pure  chromium  is 
required,  this  can  be  secured  by  fusing  together  chromic 
oxide,  chromic  carbide,  and  lime. 

In  the  Aschermann  process,  a  mixture  of  chromic  oxide 
and  antimony  sulphide  are  fused  together  in  a  graphite 
crucible,  and  from  the  resultant  alloy  of  chromium  and  anti- 
mony the  latter  element  is  removed  by  heating. 

Iron  and  Steel.  —  Under  existing  economic  conditions  it 
is  evident  that  electro-smelting  of  iron  ores  and  the  electro- 
production  of  steel  is  practically  feasible  only  where  pure  ores 
may  be  worked  and  where  electric  power  can  be  cheaply 
produced. 

There  is  no  question  but  that  an  ore  so  treated  and  a  steel 
so  produced  may  be  of  superior  quality,  at  least  when  pro- 
duced in  certain  types  of  electro-furnaces,  for  in  some  types 
of  furnace  the  influence  of  impurities  can  be  avoided  to  a 
great  extent. 

A  number  of  electric  furnaces  have  been  designed  for  the 
purpose  of  working  iron  ores  and  of  producing  steel. 

Paul  He>oult,  of  France,  was,  in  1900,  the  first  to  make  steel 
electrically  on  a  commercial  scale.  He  devised  several  kinds 
of  electro-furnaces  for  ore  smelting  and  for  steel  refining. 
One  of  these  somewhat  resembles  a  Bessemer  converter  in  its 


ELEC  TRO  TECH  NO  LOG  Y.  121 

construction,  but  contains  two  vertical  carbon  electrodes 
between  which  and  the  conducting  charge  two  arcs  are 
struck  in  series.  An  exceedingly  fine  tool  steel  can  be  pro- 
duced in  this  furnace  from  steel  scrap  and  cast  iron.  An 
alternating  current  of  60  volts  and  4000  amperes  is  used  in 
the  process. 

At  present  works  are  in  process  of  erection  at  Syracuse, 
N.Y.,  by  the  Holcomb  Steel  Company,  where  the  refining  of 
steel  will  be  done  by  the  Heroult  method.  Further  experi- 
mental work  with  the  Heroult  process  for  the  electro-smelt- 
ing of  ores  and  the  manufacture  of  steel  will  shortly  be  under 
way  at  Sault  Ste.  Marie.*  As  Canada  is  rich  in  high-grade 
iron  ores  and  commands  vast  water-power,  the  prospects  there 
for  a  successful  outcome  of  an  electro-process  of  this  kind 
are  certainly  promising. 

The  Gin  furnace  consists  of  a  zigzag-shaped  trough,  in 
which  the  premolten  cast  iron  which  is  to  experience  treat- 
ment acts  as  resistance  and  transforms  the  electric  energy 
into  heat.  The  terminals  are  hollow  steel  blocks  cooled  by 
circulation  of  water.  The  iron  is  changed  to  steel  either 
by  the  addition  of  oxide  of  iron,  or  else  by  the  introduction 
of  scrap  iron. 

In  the  Keller  furnace  the  charge  is  fed  in  from  the  top,  as 
in  a  blast  furnace.  The  electrodes,  four  or  more  in  number, 
are  inserted  vertically  and  are  independent  of  one  another; 
fusion  begins  near  the  hearth  and  extends  upwards,  the  gases 
formed  preheating  the  ores.  From  the  smelting  furnace  the 
reduced  iron  flows  into  the  steel  fining  furnace  in  which  two 
vertical  electrodes  are  used.  The  voltage  of  the  reducing 
furnace  is  about  30  volts,  of  the  steel  furnace  about  70  volts; 
in  France  about  2800  kilowatt-hours  are  required  for  making 
one  ton  of  steel  from  ordinary  ores. 

In  the  resistance  furnace  devised  by  Dr.  Borchers,  the  car- 

*.  Electrical  Review,  1905,  Vol.  47,  p.  672. 


122  NOTES  ON  ELECTROCHEMISTRY. 

bon  to  be  used  is  placed  between  the  electrodes  as  resistance, 
and  the  ore  to  be  treated  is  packed  around  this  core. 

F.  C.  Weber  has  devised  an  arc  smelting  furnace  in  which 
the  descending  charge  passes  through  a  series  of  arcs,  each 
one  of  which  can  be  independently  controlled;  this  permits 
of  an  accurate  regulation  of  temperature  in  the  various 
zones  of  the  furnace. 

Among  other  processes  devised  for  iron  and  steel  work 
mention  should  be  made  of  the  process  of  M.  Ruthenberg, 
especially  adapted  to  the  working  of  metalliferous  sands  and  of 
finely  divided  ores  at  a  relatively  small  expenditure  of  energy, 
and  of  the  process  of  Kjellin,  in  Sweden,  which,  as  previously 
mentioned,  is  s"aid  to  produce  a  steel  of  excellent  quality. 
Kjellin's  furnace  is  of  the  induction  type;  a  current  of  3000 
volts  is  supplied  and  the  current  passing  through  the  charge 
is  about  30,000  amperes.  By  avoiding  the  use  of  electrodes 
the  steel  is  not  open  to  the  absorption  of  impurities  and  hence 
the  high  grade  product.  The  cost  is  reported  to  be  compara- 
tively iow. 

Manganese.  —  A  crude  metal  containing  about  90%  of 
manganese  is  obtained  by  fusing  the  oxide  of  manganese  in  an 
arc  furnace.  As  manganese  is  rather  a  volatile  metal  the 
temperature  conditions  require  to  be  carefully  regulated,  for 
the  heat  must  not  be  allowed  to  become  too  great. 

An  iron  manganese  alloy  (ferro-manganese)  is  prepared 
by  the  Simon  process  in  France,  by  fusing  together  an  oxide 
of  manganese  and  fluorspar.  Part  of  the  electric  energy 
used  is  expended  in  electrolytic  action,  possibly  about  25% 
of  the  total  being  used  for  this  purpose,  while  the  balance 
produces  the  necessary  heating  effect.  The  ferro-manganese 
alloy  resulting  from  this  process  contains  about  85%  of 
manganese  and  from  7  to  8%  each  of  iron  and  of  carbon. 

Molybdenum.  —  Heating  molybdenum  sulphide  with  car- 
bon produces  a  crude  molybdenum  which  contains  approxi- 
mately 10%  of  impurities,  of  which  carbon  and  iron  are  the 


ELECTROTECHNOLOGY.  123 

most  important.  This  crude  metal  when  mixed  with  molyb- 
denum oxide  and  subjected  to  fusion  in  an  arc  furnace 
parts  with  its  carbon  and  is  won  in  a  pure  condition. 

Titanium.  —  The  fusing  point  of  titanium  is  higher  than 
that  of  any  metal  thus  far  obtained  by  thermo-electric 
work.  Moissan  did  not  succeed  in  completely  fusing  a 
small  amount,  possibly  350  grams,  of  a  mixture  of  titanic 
acid  and  carbon  even  by  the  expenditure  of  2200  amperes 
and  60  volts.  The  metal  titanium  combines  readily  with 
nitrogen,  but  this  compound,  the  nitride,  can  be  broken  up 
by  raising  the  temperature  of  the  arc  sufficiently  high;  in 
so  doing,  however,  some  of  the  carbon  of  the  arc  is  apt  to 
enter  into  chemical  combination  with  the  titanium,  this 
resulting  in  the  formation  of  a  carbide  of  titanium  from 
which  it  is  most  difficult,  if  not  impossible,  to  obtain  a  pure 
metal. 

Uranium.  —  This  metal  can  be  obtained  in  a  pure  state 
from  its  oxide  by  heating  the  latter  with  carbon.  Uranium 
is  volatile  in  the  electric  arc,  and  at  a  temperature  of  1000° 
C.  readily  enters  into  chemical  combination  with  nitrogen. 

Vanadium.  —  Vanadium  can  be  obtained  by  the  Gin  pro- 
cess* from  the  fluoride  of  vanadium.  The  anodes  used  are 
rods  especially  prepared  from  vanadium  trioxide,  retort 
carbon,  and  rosin,  shaped  under  hydraulic  pressure  and 
baked  at  very  high  temperatures.  The  cathode  is  made  of 
iron.  The  anode  ND100  is  approximately  200  amperes,  the 
cathode  ND100  about  600  amperes,  the  voltage  about  12 
volts. 

Alloys  with  iron,  the  so-called  ferro-vanadium  alloys,  are 
also  prepared  by  this  process. 

Tungsten.  —  Moissan  succeeded  in  preparing  this  metal  by 
fusing  together  tungstic  acid  and  pure  carbon.  It  is  impor- 
tant that  an  excess  of  carbon  be  avoided  and  that  the  temper- 

*  Bericht  des  V.  Int.  Kongresses  fur  Angew :  Chemie,  Berlin,  1903,  Vol. 
4,  p.  744. 


124  NOTES  ON   ELECTROCHEMISTRY. 

ature  be  kept  sufficiently  low  so  that  the  metal  may  not 
completely,  for  if  it  does,  some  of  the  carbon  will  enter  into 
chemical  combination  with  it,  forming  carbide  of  tungsten. 


Electro-furnaces  are  also  used  for  the  manufacture  of  other 
substances  —  not  metals  —  which,  before  the  coming  of  the 
electro -furnace  were  either  unknown,  or  were  made  by  other 
processes.  Of  these  products  the  following  should  be  men- 
tioned. 

Alundum,  or  artificial  corundum,  is  an  abrasive,  crystalline 
in  form,  and  extremely  hard  and  sharp  in  grain,  prepared  in 
the  electric  arc  furnace  from  calcined  bauxite  or  from  gibb- 
site,  by  the  Jacobs  process. 

Barium-Hydrate.  —  In  a  process  also  devised  by  C.  B. 
Jacobs,  barium  sulphate  (Barytes)  is  treated  in  an  electric 
furnace  in  the  presence  of  carbon.  The  ore  is  first  reduced 
to  barium  sulphide  and  this,  reacting  with  additional  barium 
sulphate,  forms  barium  oxide  and  sulphur  dioxide  gas.  The 
barium  oxide  is  dissolved  in  water,  and  the  hydrate  thus 
formed  is  obtained  as  crystallized  barium  hydrate  of  high 
grade  purity. 

Carbides.  —  A  class  of  bodies  termed  the  carbides  is  formed 
in  the  electric  furnace  by  reducing  the  oxides  of  some  metals 
and  non-metals  in  the  presence  of  an  excess  of  carbon.  Either 
arc  or  resistance  furnaces  may  be  used  for  the  purpose;  often 
both  systems  come  into  play  in  one  operat'on  through  the 
unavoidable  arcing  which  occurs  in  the  working  of  some 
resistance  furnaces. 

While  the  list  of  carbides  embraces  possibly  some  twenty 
odd  compounds  only  a  very  few  of  these  have  any  appreciable 
commercial  importance,  calcium-carbide  is  probably  the 
most  important  of  them  all. 

Calcium-carbide.  —  In  1892  Moissan  announced  that  he 
had  made  calcium-carbide,  a  compound  of  calcium  and  car- 


ELECTROTECHNOLOGY.  125 

bon,  by  means  of  the  electric  furnace.  Towards  the  end  of 
the  same  year,  T.  L.  Willson  stated  that  he  had,  by  fusing 
lime  and  carbon  together  electrically,  obtained  a  body  yield- 
ing acetylene  when  brought  into  contact  with  water.  This 
investigator,  it  appears,  had  made  calcium-carbide  as  early 
as  1888,  at  Spray,  North  Carolina,  but  did  publish  the  data 
at  the  time. 

The  formation  of  calcium-carbide  is  shown  by  the  for- 
mula: 

CaO  +  3  C  =  CaC2  +  CO 

When  the  current  density  through  the  resistance  core 
attains  to  1.2  amperes  per  square  mm.,  the  formation  of  the 
compound  begins  and  at  a  current  density  of  2  amperes  per 
square  mm.,  complete  fusion  is  attained  at  the  core;  the 
rest  of  the  charge,  further  removed  from  the  core,  assumes 
a  pasty  condition,  the  temperature  of  the  core  experiences  a 
gradual  lowering,  and,  in  consequence,  calcium-carbide,  the 
resultant  product,  is  intermingled  with  other  substances. 

Practically,  the  formation  of  calcium-carbide  does  not  occur 
below  a  temperature  of  2000°  C.  and  probably  a  tempera- 
ture higher  than  this  is  the  true  temperature  of  the  reaction, 
which,  as  previously  indicated,  is  partly  an  arc  and  partly  a 
resistance  reaction. 

A  slight  excess  of  carbon  should  always  be  provided,  for 
otherwise  calcium  and  carbon  monoxide  are  apt  to  be  formed 
through  the  interaction  of  the  lime  and  the  carbon  and  the 
carbide  would  in  consequence  be  exposed  to  contamination. 
In  fact,  it  is  important  to  aim  at  the  production  of  a  pure 
calcium-carbide  from  the  outset,  because  this  carbide  when 
once  formed  is  practically  neither  fusible  nor  soluble,  and 
therefore  offers  great,  if  not  insurmountable,  difficulties  to 
Any  subsequent  purification. 

To  obtain  as  pure  a  calcium-carbide  as  possible  the  addi- 
tion, before  fusion,  of  manganese  peroxide  and  of  calcium 


126  NOTES  ON  ELECTROCHEMISTRY. 

carbonate  to  the  original  charge  of  lime  and  carbon  has  been 
advocated;  this  process  is  known  as  the  Hewes  process.  In 
another  process,  devised  by  Rathenau,  iron,  or  oxide  of  iron, 
is  added  to  the  charge  before  fusion  so  that  the  iron  may 
combine  with  and  remove  all  of  the  silicon  present  as  ferro- 
silicon. 

In  the  manufacture  of  calcium-carbide,  either  the  direct  or 
the  alternating  current  may  be  used;  for  some  reasons  the 
latter  is  preferable. 

The  commercial  value  of  a  given  calcium-carbide  depends, 
of  course,  upon  the  amount  of  acetylene  gas  (C2H2)  which  it 
will  yield  on  reacting  with  water.  The  equation  reads: 

CaC2  +  2  H2O  =  C2H2  +  Ca  (OH)2 

The  theoretical  yield  of  one  kilogram  of  pure  calcium- 
carbide  is  about  350  liters  of  acetylene  gas,  at  normal  tem- 
perature and  pressure ;  from  the  commercial  product,  however, 
generally  not  more  than  85%  of  this  yield  are  obtained. 

Carbon  bi-sulphide.  —  E.  R.  Taylor,  at  Penn  Yan,  New 
York,  produces  carbon  bi-sulphide  in  electric  furnaces.  These 
measure  about  41  feet  in  height  and  16  feet  in  diameter,  the 
diameter  decreasing  towards  the  top.  These  furnaces  are  con- 
structed of  a  steel  shell  and  are  lined  with  refractory  fire  brick 
or  some  similar  substance. 

The  electrodes,  four  in  number,  are  placed  90°  apart  and 
are  re-enforced  in  the  interior  of  the  furnace  by  a  continuous 
supply  of  coke  or  broken  carbons,  which  are  fed  into  the 
furnace  by  conduits. 

The  sulphur  is  placed  at  the  bottom  of  the  working  chamber 
o^  the  furnace  and  extends  up  to  and  around  the  electrodes. 
Annular  chambers  situated  in  the  lower  part  of  the  furnace 
are  kept  supplied  with  sulphur,  which  is  fed  in  at  the  top  and 
which  runs  down  into  the  furnace  in  a  molten  condition. 

The  vapors  of  sulphur  passing  through  the  charcoal, — 
which  fills  the  body  of  the  furnace,  combine  with  it  and  form 


ELECTROTECHNOLOGY.  127 

vapor  of  carbon  bi-sulphide;  this  passes  off  through  a  tube 
near  the  top  of  the  furnace  into  a  condenser,  wherein  the  vapor 
becomes  liquefied.  A  subsequent  distillation  insures  a  product 
almost  entirely  pure. 

The  furnaces  are  arranged  with  a  view  to  economize  most  of 
the  heat  generated  in  the  process  and  are  continuous  in  their 
action.  The  output  is  about  4500  kilograms  of  carbon  bi- 
sulphide in  24  hours.  The  working  power  is  furnished  by  tur- 
bine water-wheels,  although  a  steam  engine  is  held  in  reserve 
in  case,  for  any  reason,  the  water  power  should  fail. 

Glass.  —  Glass  when  in  a  fused  condition  is  an  electrolyte, 
and  a  number  of  electro  thermic  processes  have  been  devised 
for  its  manufacture.  In  some  of  these  processes  as  in  the 
Shade  process,  an  arc  furnace  is  employed,  in  which  between 
four  and  six  kilowatt-hours  are  required  to  produce  one 
kilogram  of  molten  glass. 

In  other  processes,  for  instance,  in  that  of  Reich,  a  resis- 
tance furnace  is  used.  In  a  recently  designed  furnace  of  the 
resistance  type,  kryptol  —  which  is  essentially  pure  carbon 
of  uniform  grain,  is  utilized  as  the  heating  material.*  The 
kryptol  is  packed  around  the  vessel  holding  the  charge  of 
glass  and  by  this  arrangement  the  loss  of  heat  by  radiation  is 
materially  reduced.  Carbon  electrodes  are  employed,  the 
current  used  is  about  100  volts,  and  the  operation  is  carried 
on  at  a  temperature  materially  below  that  of  an  arc  furnace. 

In  still  other  furnaces  for  the  manufacture  of  glass,  a  com- 
bination of  the  arc  and  the  resistance  principle  is  employed; 
an  illustration  of  this  type  is  the  August  Voelker  furnace, 
which  is  used  in  Germany  and  which  is  reported  to  be  very 
effective  in  its  working. 

Graphite.  —  Artificial  graphite  f  is  another  product  made 
by  the  Acheson  Company  at  Niagara  Falls.  It  is  prepared  in 

*  Electrical  Review,  1905,  Vol.  47,  p.  445. 

t  Consult  C.  P.  Townsend,  Electric  World,  1901,  for  an  historical 
resum3  of  studies  on  artificial  graphite. 


128  NOTES  ON  ELECTROCHEMISTRY. 

a  resistance  furnace  from  anthracite  coal  or  from  coke.  The 
charge  is  separate  from  the  core,  which  consists  of  carbon 
rods  extending  through  the  charge.  At  the  beginning  of  the 
operation  these  carbon  rods  transmit  the  whole  of  the  current 
and,  in  consequence,  become  highly  heated.  The  high  tem- 
perature thus  generated,  converts  that  portion  of  the  charge 
immediately  adjacent  to  the  core  into  graphite;  this  graphite 
then  conducts  a  part  of  the  current  and  thus  gradually  the 
zone  of  reaction  extends  farther  and  farther  through  the 
mass. 

The  Acheson  Company  also  graphitize  electrodes,  these  in 
the  process  being  exposed  to  a  temperature  above  the  temper- 
ature of  volatilization  of  silicon,  iron,  and  aluminium. 

Nitrogen  Fixation.  —  Chemical  combination  of  atmospheric 
nitrogen  and  oxygen,  and  the  union  of  the  resultant  nitrogen- 
oxides  with  water  to  form  nitric  acid,  has  been  achieved  by 
F.  C.  Crocker,  C.  S.  Bradley,  and  D.  R.  Lovejoy. 

The  works  are  situated  at  Niagara  Falls.  Dry  air  is  passed 
through  a  chamber  provided  with  stationary  negative  elec- 
trodes which  are  placed  in  vertical  rows  and  before  which 
there  revolves  a  central  shaft  carrying  the  positive  electrodes 
ending  in  fine  platinum  wires.  The  negative  terminals  are  in 
connection  with  choke-coils  which  are  kept  submerged  in  oil. 
A  current  of  10,000  volts  is  employed,  and  about  69,000  arcs 
per  minute  are  flashed  through  the  air  which  passes  between 
the  electrodes.  The  treated  air  contains  between  two  and 
three  per  cent  of  nitrogen  oxides.  Seven  HP.  hours  are  said 
to  produce  about  one-half  kilogram  of  nitric  acid;  this  acid 
and  calcium  nitrate  —  valued  as  a  fertilizer,  are  among  the 
products  manufactured  at  the  Niagara  Falls  plant.* 

Oxone. —  Oxone,  a  fused  peroxide  of  sodium,  is  manufactured 

*  For  a  recent  comprehensive  review  of  the  work  done  on  atmos- 
pheric nitrogen  see: 

A.  Neubur^er,  Die  Verwerthung  des  Luftstickstoffs,  Zeitschrift  fur 
Angeioandt*  Chemie.,  1905,  pp.  1761,  1810,  1843. 


ELECTROTECHNOLOG  Y.  1 29 

by  the  Niagara  Electrochemical  Company.*  It  is  a  stony 
compound  which  yields  oxygen  gas  when  brought  into  contact 
with  water.  It  is  employed  for  therapeutical  purposes  and 
its  use  for  the  sterilization  of  foods  has  also  been  recom- 
mended. Analogous  peroxides  exist  of  calcium,  magnesium, 
and  zinc. 

Phosphorus.  —  Various  furnaces  have  been  devised  for  the 
electro-winning  of  phosphorus  and  a  large  proportion  of  the 
world's  supply  of  this  article  is  now  obtained  by  electro- 
thermic  methods. 

In  the  Readman  and  Parker  process,  mineral  phosphate, 
finely  ground,  is  mixed  with  sand  and  carbon  and  intro- 
duced into  a  furnace  from  which  all  air  is  carefully  excluded. 
This  furnace  is  of  the  resistance  type;  the  electrodes  are 
made  of  carbon  and  enter  the  lower  part  of  the  furnace, 
the  hearth.  The  phosphorus  is  caught  under  water  as  it 
distils  from  the  furnace. 

In  the  Machalske  process  an  arc  furnace  is  used  and  an 
alternating  current  is  employed.  Tri-calcium-phosphate, 
silica,  and  carbon  are  the  crude  materials  used,  phosphorus, 
carbon-monoxide,  and  a  slag  of  calcium  silicate  are  pro- 
duced. 

Silicides. — The  silicides  are  a  class  of  compounds  similar 
in  type  to  the  carbides,  but  with  silicon  in  the  place  of  carbon. 

The  silicides  of  calcium,  barium,  and  strontium,  expressed 
respectively  by  the  formula:  CaSi2,  BaSi2,  SrSi2,  were  dis- 
covered by  C.  B.  Jacobs  and  are  all  manufactured  by  The 
Ampere  Electrochemical  Company. f 

To  prepare  these  compounds  the  silicates  of  the  above- 
mentioned  alkaline  earth  metals  are  reduced  in  the  electric 
furnace  in  the  presence  of  sufficient  carbon,  or,  a  mixture  may 
be  made  of  carbon  and  silica,  together  with  some  of  the  salts 

*  F.  A.  J.    FitzGerald,  Electrochemical  and  Metallurgical  Industry, 
Vol.  3,  1905,  p.  253. 

t  Jacobs,  American  Institute  of  Electrical  Engineers,  1902.      j 


130  \OTKS  ON  ELECTROCHEMISTRY. 

of  the  metals  mentioned  and  the  mixture  fused  in  the  electric 
furnace. 

These  silicides  are  crystalline  in  structure;  when  brought 
into  contact  with  water  they  decompose  it,  and  yield  a  silico- 
hydrate  of  the  metal  and  free  hydrogen  gas.  Of  the  silicides 
mentioned  a  given  weight  of  calcium  silicide  furnishes  the 
greatest  volume  of  hydrogen  gas,  a  corresponding  amount  of 
barium  silicide  will  yield  only  about  one-half  as  much. 
Commercially,  these  compounds  are  used  in  the  preparation 
of  hydrogen  gas,  and  they  are  also  employed  as  powerful 
reducing  agents. 

Copper  silicide  (CuSi)  is  another  member  of  this  group; 
it  is  principally  used  as  a  reducing  agent  in  the  preparation 
of  a  certain  class  of  copper  alloys,  the  so-called  silicon  bronzes. 
Copper  silicide  contains  about  30%  of  silicon. 

Ferro-silicon  can  be  made  from  the  slags  of  steel  furnaces. 
Two  ferro-silicon  alloys,  the  one  containing  about  30%  and 
the  other  about  50%  of  silicon  and  approximately  5%  of 
carbon,  are  used  in  the  manufacture  of  steel,  especially  of 
armor  plate.  Ferro-silicon  is  far  more  effective  than  carbon 
as  it  evolves  7800  calories,  where  a  corresponding  amount 
of  carbon  yields  approximately  but  2500  calories. 

Silicon  Carbide.  —  Technically  known  as  carborundum, 
silicon  carbide  (SiC)  is  produced  by  the  fusing  of  sand  and 
carbon,  as  expressed  by  the  equation: 

SiO2  +  3  C  -  SiC  4-  2  CO 

Acheson  first  made  carborundum  in  1893.  The  operation 
is  conducted  in  a  furnace  built  up  of  loose  brick,  and  each 
furnace  serves  for  one  run  only.  An  alternating  current  is 
conveyed  by  leads  to  bronze  end-plates  to  which  the  carbon 
electrodes,  bundles  of  carbon  rods,  are  attached;  between 
these  electrodes  the  core  of  coarsely  powdered  coke  is  laid. 
The  charge,  consisting  of  sand,  coke,  sawdust,  and  a  little 
salt,  is  placed  about  this  core.  Each  furnace  takes  about 


ELECTROTECHNOLOGY.  131 

1000  HP.  The  initial  voltage  is  about  200  volts,  but  this 
drops  by  fully  60%  as  the  heating  of  the  core  progresses. 
The  total  process  takes  from  twenty-four  to  twenty-six  hours, 
that  is  to  say,  the  electric  current  is  passed  for  that  length 
of  time,  then  the  furnace  is  allowed  to  cool  and  is  dis- 
mantled. 

Various  products  are  formed,  segregated  in  layers.  The 
central  core  is  graphite,  next  to  this  a  layer  of  crystallized 
carborundum,  and  then  a  layer  of  greenish  silicon  carbide, 
amorphous  in  structure,  generally  intermingled  with  some  of 
the  original  charge  which  has  not  been  transformed.  This 
substance,  essentially  a  compound  of  carbon  and  silicon,  is 
termed  white  stuff;  all  of  the  material  beyond  the  white  stuff 
is  reincorporated  with  the  next  charge.  The  manufacture 
of  white  stuff  has  been  made  the  subject  of  a  separate  patent 
by  Acheson. 

Carborundum  consists  practically  of  70%  of  silicon  and 
30%  of  carbon;  it  is  apt  to  hold  as  impurities  some  iron, 
aluminium,  and  calcium. 

About  8.6  kilowatt-hours  are  required  to  produce  one  kilo- 
gram of  carborundum  and  the  temperature  must  be  carefully 
regulated  to  guard  against  volatilization  of  the  silicon; 
3800°  C.  is  approximately  the  temperature  of  formation  of 
carborundum.*  This  substance  is  used  largely  as  an  abrasive, 
for  furnace  linings,  and  for  purposes  of  deoxidation  in  the 
manufacture  of  steel. 

Siloxicon.  —  This  substance,  originally  obtained  as  a  by- 
product in  the  production  of  carborundum  is  now  a  separate 
article  of  manufacture.  It  is  a  chemical  compound  of  the 
elements  carbon,  silicon,  and  oxygen,  and  its  constitution  is 
expressed  by  the  formula,  Si2C2O. 

It  is  made  at  a  temperature  of  about  2700°  C.,  in  furnaces 
similar  in  construction  to  those  used  in  the  manufacture  of 

*  J.  Wright,  Liber  cit.  p.  42.  Confer;  F.  A.  J.  FitzGerald,  Electrochemi- 
cal and  Metallurgical  Industry,  1906,  p.  53. 


1,32  NOTES  ON  ELECTROCHEMISTRY. 

carborundum.  Siloxicon  is  very  refractory  at  high  tempera- 
tures and  is  soluble  only  in  hydrofluoric  acid;  as  it  is  self- 
binding  it  needs  only  to  be  moistened  with  water  and  can  then 
be  molded  into  any  shape  desired,  preliminary  to  firing.  It 
is  used  for  the  manufacture  of  fire-bricks,  crucibles,  etc. 

ELECTRO-ORGANIC  PROCESSES. 

B.I.  Direct  Action  Processes.  —  Electro-reactions  in  the 
domain  of  organic  chemistry,  may  also  be  divided  into  direct 
action  and  into  indirect  action  processes.  The  former  group 
would  include  all  actions  in  which  electrical  energy  is  directly 
applied,  for  instance,  all  electrolytic  processes  —  whether 
these  be  processes  of  substitution,  oxidation,  or  reduction; 
it  would  also  embrace  reactions  effected  by  silent  discharge. 
The  other  group  would  include  all  indirect  effects  such  as 
thermo-electric  and  photo-electric  processes. 

Speaking  of  the  first  of  these  groups,  attention  has  been 
given  chiefly  to  processes  of  reduction  for  the  reason  that 
these  can  be  most  conveniently  studied  with  reference  to 
certain  groups  in  the  molecule,  whereas  processes  of  oxida- 
tion are,  as  a  rule,  apt  to  involve  the  molecule  as  a  whole  in 
chemical  change. 

Reference  cannot  here  be  made  in  detail  to  the  many 
interesting  and  valuable  results  obtained  in  organic  chemis- 
try by  processes  of  electro-analysis  and  electro-synthesis, 
which  afford  the  great  advantage  of  permitting  the  bringing 
about  of  chemical  reactions  without  necessitating  the  intro- 
duction of  any  chemical  reagents.  It  must  suffice  to  remark 
that  within  the  past  decade  great  advances  have  been  made 
in  the  application  of  electrical  energy  to  the  solving  of  numer- 
ous problems  in  organic  chemistry  and  that  the  field  is  still 
a.  very  promising  one  for  the  investigator.* 


C.  W.  Loeb,  Die  Elektrochemie  der  Organischen  Verbindungen, 
1905. 


ELECTROTECHNOLOGY.  133 

Among  electro-technological  operations,  dealing  with  the 
manufacture  of  organic  substances,  there  should  be  cited  the 
preparation  of  fine  chemicals  and  of  dye-stuffs;  among  the 
chemicals  thus  made  there  may  be  mentioned,  vanillin  (from 
iso-eugenol),  iodoform,  chloroform,  and  bromoform;  among 
the  dye-stuffs  so  prepared,  aniline,  alizarin-black  and  fast 
yellow  dyes. 

Experiments  looking  to  the  application  of  electrical  energy 
to  agricultural  problems  were  tried  many  years  ago,  and  a 
number  of  attempts  have  been  made  to  foster  the  growth  and 
the  yield  of  crops  by  stimulating  the  soil  by  electricity. 

Thus  Spechnew,  in  1889,  exposed  seeds,  after  they  had 
been  immersed  in  water,  to  the  action  of  induction  currents 
and  secured  their  germination  in  from  two  to  eight  days, 
while  control-seeds  which  had  not  been  treated  with  elec- 
tricity, required  from  four  to  fifteen  days  before  they  germi- 
nated. These  results  were  confirmed  by  other  investigators, 
and  several  cases  are  on  record  where  it  was  found  that  both 
the  yield  and  the  growth  of  flowers  and  vegetables  were 
remarkably  improved  and  stimulated  by  passing  electric 
currents  between  large  copper  electrodes  buried  in  the  soil. 
Interesting  results  along  such  lines  were,  among  others, 
obtained  by  the  Hatch  Experimental  Station  in  Amherst, 
Mass.,  as  early  as  1892. 

B.  II.  Silent  Discharge  Processes. —  In  the  silent  electric 
discharge,  electrical  energy  is  continuously  passing  from  one 
conductor  to  another  through  an  intervening  space  which  is 
filled  with  a  gas  or  with  a  mixture  of  gases. 

The  apparatus  employed  for  silent  discharge  work  can  be, 
and  is,  constructed  in  various  forms,  but  the  essential  feature 
of  construction  in  all  of  them  is  an  arrangement  which  obliges 
the  electric  discharge  to  pass  through  a  layer  of  the  gas  acted 
upon. 

Frequently  the  current  is  passed  between  two  layers  of 
sulphuric  acid  contained  in  very  thin  glass  vessels,  the  elec- 

7 


134  NOTES  ON  ELECTROCHEMISTRY. 

trical  energy  being  obliged  to  pass  through  the  containing 
glass  walls  and  through  the  gas  confined  between  them.  In 
other  forms  of  apparatus  a  metallic  foil  —  tin-foil,  aluminium- 
foil  or  silver,  is  used  instead  of  the  acid  conductors.  The 
simplest  form  of  apparatus  used  for  the  purpose  consists  of 
two  metal  plates  between  which  the  gas  to  be  acted  upon  is 
placed;  as  these  metal  plates  are,  however,  apt  to  become 
worn  and  roughened  by  the  discharges,  there  is  always 
some  danger  of  spark  discharges.  Aluminium  is  possibly  the 
metal  best  suited  for  constructions  of  this  description. 

In  every  case  the  thinner  the  layer  of  gas  through  wh'ch 
the  electric  discharge  must  pass,  the  more  effective  is  the 
reaction.  In  rarefied  gases  the  discharge  is  often  accom- 
panied by  luminous  phenomena,  the  so-called  Geissler  tube 
effects. 

As  there  is  no  appreciable  elevation  of  temperature  in  these 
reactions,  endo thermic  compounds  may  be  formed  under  the 
influence  of  the  silent  discharge,  arid  for  this  reason  these 
phenomena  and  reactions  are  of  the  greatest  value  in  bring- 
ing about  simple  organic  syntheses,  similar  to  those  which 
plants  effect  under  the  influence  of  sunlight. 

Berthelot,  experimenting  with  the  silent  discharge,  showed 
that  atmospheric  nitrogen  could  be  bound  in  the  form  of 
complex  organic  compounds,  which,  when  treated  with 
soda-lime  at  high  temperatures  yielded  ammonia.  The 
results  he  obtained  are  of  special  interest,  as  they  point  to  the 
possibility  of  the  assimilation  of  atmospheric  nitrogen  by 
plants  under  the  influence  of  atmospheric  electricity. 

Thus  Berthelot*  pointed  out,  that  in  clear  weather  there 
is  a  difference  of  potential  of  from  20  to  30  volts  between 
two  layers  of  air  which  are  but  one  meter  apart,  and  in  rain 
storms  this  difference  of  potential  may  rise  to  about  500 
volts.  As  Berthelot  achieved  a  fixation  of  nitrogen  by  carbo- 
hydrates by  means  of  a  difference  of  potential  of  8  volts  only, 

*  Compt.  rend.  1900,  Vol.  131,  p.  772. 

V 


ELECTROTECHNOLOGY.  135 

his  suggestion,  that  in  nature  the  silent  discharge  is  an  active 
agent  in  plant-life  and  growth  is  certainly  most  plausible. 

A  number  of  synthetic  reactions  have  been  achieved  in  the 
laboratory  by  means  of  the  silent  discharge.  Thus,  under  its 
influence,  carbon  monoxide  and  nitrogen  have  been  made  to 
yield  formaldehyde  and  marsh-gas  (Brodie,  1872),  and,  it  is 
interesting  to  recall  that  formaldehyde  was  used  by 
Butlerow  more  than  forty  years  ago  in  the  synthesis  of 
sugars. 

Collie*  found  that  carbon  dioxide  is  readily  converted  into 
oxygen  and  carbon  monoxide  under  low  pressure  electric 
discharge,  and  he  too  calls  attention  to  the  analogy  between 
the  action  of  the  silent  discharge  and  the  action  of  light  in 
plant  life;  the  polymerizing  effects  of  the  silent  discharge  are 
especially  notable. 

The  action  of  this  agent  is  certainly  in  part  electrothermic' 
and,  possibly,  in  part  electrolytic,  although  it  is  well  known 
that  the  output  of  any  product  secured  by  means  of  the  silent 
discharge  does  not  conform  to  the  theoretical  yield  which 
would  be  expected  were  the  reaction  governed  by  Faraday's 
laws.  In  the  light  of  Our  present  knowledge  it  seems  most 
probable  that  in  the  silent  discharge  vast  amounts  of  kinetic 
energy  transformable  into  chemical  energy  are  introduced 
into  the  system  by  speeding  electrons.! 

The  principal  technological  application  of  the  silent  dis- 
charge is  the  generation  of  ozone,  by  the  process  of  Siemens 
and  Halske.  A  metal  tube,  cooled  by  water,  is  inserted  in 
a  tube  made  of  mica  which  is  wound  with  copper  ribbon.  The 
annular  space  between  the  two  tubes  is  but  narrow,  and  serves 
for  the  passage  of  the  air,  the  oxygen  of  which  is  to  be  trans- 
formed into  ozone.  The  silent  discharge  passes  between  the 
metal  cylinder  and  the  copper  ribbon  on  the  mica  cylinder; 

*  J.  N.  Collie,   "Syntheses  by  Means   of  the  Silent   Electric   Dis- 
charge."     Trans.  Journ.  Chem.  Soc.,  London,  1905,  p.  1540. 
t   W.  Loeb,  Liber  cit.  p.  279. 


136  NOTES  ON  ELECTROCHEMISTRY. 

a  series  of  such  double  tubes  are  combined  to  form  a  sort  of 
lattice  work.  An  alternating  current  is  employed;  about  65 
volts  are  transformed  into  6500  volts,  and  about  18  grams  of 
ozone  are  produced  per  electric  HP.  hour;  this  amounts  to 
practically  nine  times  the  amount  which  could  be  secured 
if  this  reaction  were  electrolytic  in  character. 

Jt  is  estimated  that  in  the  best  of  ozone-generating  plants, 
riot  more  than  15%  of  the  total  energy  supplied  is  con- 
sumed in  bringing  about  the  transformation  of  oxygen  into 
ozone. 

B.  III.  Electro-Osmosis.  —  If  a  porous  diaphragm  be  intro- 
duced into  an  electrolyte  and  a  sufficiently  high  voltage  be 
employed,  the  contents  of  one  electrode  chamber  will  be  forced 
bodily  through  the  diaphragm  into  the  other  electrode 
chamber  until  a  certain  difference  of  pressure  will  have  been 
established  between  the  solutions  in  the  two  compartments. 

Electro-osmosis,  or  kataphoresis,  as  it  is  also  termed,  has 
been  known  for  a  long  time  and  was  submitted  to  careful 
study  by  G.  Wiedemann  as  early  as  1852.*  This  phenome- 
non is  entirely  different  from  that  of  osmosis,  for  in  kata- 
phoresis the  whole  solution  passes  through  the  diaphragm 
unchanged,  whereas  in  osmosis  only  the  solvent  passes,  not 
the  solute.  The  phenomena  of  kataphoresis,  as  recognized 
by  Hittorf,  are  also  independent  of  electrolytic  action  and' 
are  not  subject  to  the  laws  of  Faraday,  although  electrolytic 
phenomena  probably  accompany  the  process  to  a  certain 
extent. 

In  aqueous  solutions,  as  a  rule,  the  solution  travels  through 
the  diaphragm  from  the  anode  to  the  cathode  compartment,- 
although  in  certain  instances  the  direction  of  this  flow  is 
reversed;  the  nature  of  the  solution  and  the  nature  of  the 
diaphragm  seem  to  be  the  determining  factors  in  this  matter; 
The  cause  of  kataphoresis  is  probably  the  taking  on  of  oppo- 

*  G.  Breaig,  Ber.  ties  V.  Iiit.KongressesfiirAngewandteChemie,  1903, 
Vol.  4,  p.  643. 


ELECTROTECHNOLOGY.  137 

site  electric  charges  by  the  walls  of  the  diaphragm  and  by  the 
particles  of  the  solution  passing  through  it. 

If  no  diaphragm  is  used,  but  if  very  finely  divided  particles 
of  some  solid  or  colloid  are  suspended  in  a  poorly  conducting 
fluid  and  an  electric  current  passed  through,  then  the  parti- 
cles of  the  solid  and  the  particles  of  the  fluid  medium  in 
which  these  are  suspended  will  assume  opposite  electric 
charges,  and  the  solid  particles  will  be  set  in  motion.  In  a 
general  way  it  may  be  stated,  that  substances  which,  in  a 
finely  divided  state,  take  on  a  charge  electronegative  to  water 
will  travel  to  the  anode;  if  such  substances  are  made  into 
a  diaphragm,  they  will  induce  water  to  travel  to  the  cathode. 

An  application  of  kataphoresis  —  causing  a  tanning  solu- 
tion to  penetrate  into  and  effect  the  tanning  of  hides,  has 
resulted  in  a  great  saving  of  time  compared  with  the  time 
required  in  the  former  methods  of  doing  this  work. 

The  first  attempts  in  this  direction  seem  to  have  been  made 
as  early  as  1850,  by  Cross;  however,  his  results  do  not  appear 
to  have  been  very  satisfactory.  Since  that  time  a  consider- 
able number  of  electro-tanning  processes  have  been  devised; 
in  the  process  of  L.  A.  Groth,  in  which  the  hides  are  kept  in 
motion  in  a  direction  at  right  angles  to  the  electric  current 
passing,  it  has  been  found  that  a  treatment  of  eight  hours 
will  give  results  equivalent  to  those  secured  by  a  full  month's 
tanning  according  to  the  old  method. 


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NAME  INDEX. 


Addicks,  96 
Ampere,  17 
Arrhenius,  28,  41,  44,  46 

Bancroft,  104 
Beccaria,  22 
Becker,  112 
Becquerel,  11,  95 
Be'mont,  11 
Berthelot,  134 
Berzelius.  25,  26 
Bradley,  128 
Bredig,  63,  136 
Brodie,  135 
Brugnatelli,  25 
Bucherer,  112 
Buff,  29 

Calvert,  45 
Carlisle,  24 
Cavendish,  22 
Clausius,  27,  28,  46 
Clifford,  10 
Collie,  135 
Collins,  32 
Cormack,  49 
Coulomb,  18 
Cowles,  116 
Cowper-Coles,  96 
Crocker,  34,  128 
Crookes,  10,  11 
Cross,  137 
Cruickshank,  25 
Curie,  11 
Cuthbertson,  23 


Dalton,  26 
Davy,  25,  20 
De  Chalmont,  116 
)eimann,  23 
De  Laplace,  23,  37 
Dufaye,  9 

Ebert,  14 
Elkington,  95 

Fabroni,  24 

Faraday,  19,  27,  52,  62 
FitzGerald,  129,  131 
Foerster,  109 
Franklin,  9 
Fromm,  105 

Galvani,  24 
Getman,  65 
Gilbert,  8 
Groth,  137 
Grothuss,  25,  27 
Guthe,  32 

Hall,  112 
Hay  den,  96 
Heirnwood,  32 
Henry,  20,  24 
Heroult,  120 
Hess,  37 
Kissinger,  25 
Hittorf,  C3,  04,  136 
Hopkins,  47.  60 


Jacobi,  103 
Jacobs,  129 


139 


140 


NAME  INDEX 


Jahn,  38 
Jordan,  103 
Joule,  4,  20 

Kahle,  32 

Kahlenberg,  58 

Keller,  97 

Kelvin,  38 

Kohlrausch,  32,  33,  60,  02 

La  Cour,  119 
Lavoisier,  3,  23,  37 
Le  Blanc,  78 
Lodge,  44,  65 
Loeb,  132,  135 
Lorenz,  62 
Lovejoy,  128 

Marchese,  94 
Maxwell,  3 
Mayer,  3,  4 
Moissan,  116,  123,  124 
Murray,  103 
Mylius,  105 

Nernst,  29,  45,  54,  63,  70 
Neuburger,  128 
Nicholson,  24 

Ohin,  17 

Ostwald,  29,  45,  50,  63 

Patterson,  32 
Planck, 28 
Plante",  77 
Potter,  117 
Priestley,  22 


Ramsay,  13 
Rayleigh,  32,  33 
Richards,  30,  32,  91,  112 
Rontgen,  11 
Rutherford,  13 

Schmidt,  11 
Sedgewick,  32 
Siemens,  115 
Smith,  53 
Soddy, 13 
Spechnew,  133 
Spencer,  103 
Stoney,  10 
Streintz,  77 
Symmer,  9 

Taylor,  126 
Thomson,  10,  26,  45 
Townsend,  127 

Van  Maruni,  22 
Van  Troostwijk,  23 
Van't  Hoff,  28,  41,  42,  44 
Volta,  17,  23,  24 
Von  Helmholtz,  28 

Walker,  49,  52 
Watt,  19 
Whetham,  3,  65 
Wiedemann,  136 
Williamson,  46 
Willson,  125 
Winkler,  87 
Wollaston,  25 
Wright,  131 

Young,  3 


SUBJECT    INDEX. 


Absolute  units,  6,  21 
Accumulators,  75,  77,  78 
Acetylene  gas  yield,  126 
Acheson  furnace,  116 
Acheson  process,  130 
Acid,  definition,  50 
Acidity,  51 
Acker  process,  1 14 
Alkali  metals,  isolation,  26 
Alpha-rays,  11 
Aluminium,  111 
Aluminium  production,  112 
Alundum,  124 
Ammeter,  79 
Ampere,  definition,  16 
Ampere-hour,  definition,  18 
Anion,  definition,  46 
Arc  furnaces,  115 
Aschermann  process,  120 
Ashcroft  process,  102,  114 
Atmosphere,  electrification,  14 

Barium  hydrate,  124 
Base,  definition,  50 
Basicity,  61 
Bell  process,  106, 108 
Berzelius'  theory,  26 
Beta-rays,  12 
Betts'  process,  100 
Borcher' s  furnace,  117,  121 
Browne's  process,  101 
Buiisen  cell,  76'        ; 


Calcium  carbide,  124 
Calorie,  20,  38 
Capacity  factor,  14,  35 
Carbides,  124 
Carbon  bi-sulphide,  126 
Carborundum,  130 
Carnallite,  113 
Castner  process,  109,  113 
Cathion,  definition,  46 
Cells,  electric,  75,  76 
C.  G.  S.  system,  6,  6 
Chemical  equivalent,  27,  31 
Chemical  polarization,  74 
Chlorates,  production,  107 
Chlorine  and  alkali-hydrates,  106 
Chromic  acid  cell,  76 
Chromium,  120 
Clark  cell,  36,  38 
Concentration  polarization,  73 
Conductivity,  equivalent,  61 
Conductivity,  molecular,  60 
Conductivity,  specific,  62 
Conductivity,  unit,  59 
Constantan,  81 
Conductors  of  electricity,  15 
Copper,  94 

Copper  output  calculation,  97 
Corundum,  artificial,  124 
Coulomb,  definition,  18 
Coulometers,  29,  30 
Cross-section  of  wires,  84 
Current  amount,  calculation,  34 


141 


142 


SUBJECT  INDEX. 


Current  density,  74,  87 
Current  measurement,  79 
Current  regulation,  81 
Current  sources,  75 

Daniell  cell,  38,  76 

Davy's  electrochemical  theory,  26 

Deduction,  2 

Depolarizers,  68 

Diaphragm  process,  106,  107 

Dielectric  constant,  45 

Dissociants,  49 

Dissociation  voltage,  37,  73 

Eddy  furnace,  118 
Edison  accumulator,  78 
Edison  primary  cell,  76 
Electric  arc,  temperature,  119 
Electric  conductors,  15 
Electric  current,  nature,  10 
Electric  energy,  8,  14 
Electric  light  current,  75,  77 
Electric  power,  calculation,  34 
Electric  pressure,  16 
Electric  theory,  Berzelius',  26 
Electric  units,  absolute,  21 
Electric  units,  practical,  21 
Electric  valencies,  46 
Electricity,  animal,  24 
Electricity,  contact  theory,  24 
Electricity,  galvanic,  24, 
Electricity,  nature,  23 
Electricity,  properties,  14 
Electricity,  theories,  8 
Electro-affinity,  48,  73 
Electro-analysis,  66 
Electrochemical  equivalent,  31,32,  33 
Electrochemical  sequence,  47 
Electrochemical  theory,  Davy's,  26 
Electrochemistry,  evolution,  22 
Electrode-areas,  calculation,  86 


Electrodes,  84 
Electrode  potential,  74 
Electrodepositiou  from  fused  electro- 
lytes, 110 

Electrodeposition  from  solution,  94 

Electro -furnaces,  114 

Electro-furnace  products,  119 

Electro- organic  processes,  132 

Electro-osmosis,  156 

Electrolyte,  28 

Electrolytes,  fused,  110 

Electrolytic  cell,  resistance,  83 

Electrolytic  dissociation,  28,  41 

Electrolytic  dissociation  theory,  ob- 
jections, 58 

Electrolysis,  28 

Electrolytic  solution  pressure,  70 

Electromotive  force,  35,  72 

Electron,  8,  10 

Electron  theory,  10 

Electro-plating,  103 

Electrotechnology,  93 

Electrothermic  processes,  114 

Electrotyping,  103 

Electrozincing,  105 

Elements,  electrochemical 
sequence,  47 

Energetics,  laws,  4 

Energy,  conservation,  3 

Energy,  dissipation,  6 

Energy  efficiency,  92 

Energy  factors,  4 

Energy,  forms,  4 

Equivalent  conductivity,  61 

Evolution  of  electrochemistry,  22 

Farad,  definition,  19 
Faraday,  definition,  32 
Faraday's  laws,  29,  67 
Faraday's  researches,  27 
Forms  of  energy,  4 
Fused  electrolytes,  110 


SUBJECT  INDEX. 


Gamma-rays,  12 

Gas-equation,  42 

General  principles  of  science,  1 

Gin  furnace,  121 

Gin  process,  123 

Glass,  127 

Gold,  99 

Goldschinidts'  process,  102 

Grain  equivalent,  31 

Graphite,  127 

Griesheira— Electron  process,  108 

Hall  aluminium  process,  111 

Hargreaves  and  Bird  process,  108 

Heat  equivalent,  20 

Heat  of  formation,  37 

Heat  summation,  37 

Helium,  13 

Henry,  definition,  20 

Heraeus  furnace,  118 

Heroult  aluminium  process,  111 

He"roult  steel  process,  120 

Hewes  process,  126 

Hittorf's  number,  64 

Hoepfner  processes,  95,  102,  103 

Horse-power,  definition,  19 

Hydrolysis,  56 

Hypochlorites,  production,  107 

Hypothesis,  definition,  2 

Indicators,  theory,  54 

Induction,  2 

Induction  furnace,  117 

Intensity  factor,  14,  35 

Ion,  definition,  45 

Ions,  existence  in  electrolytes,  46 

Ions,  migration,  63 

Ions,  mobility,  63 

Ions,  nomenclature,  62 

Ion  reactions,  50 

Ion  symbols,  52 

Ion  theory,  41 

Ion-velocity  measurement,  65 


lonization,  degree,  49 
lonization  of  water,  51 
lonogen,  63 
Iron  and  steel,  120 
Irreversible  cells,  69 

Jacobs  process,  124 
Joule,  definition,  20 
Joule,  heat  equivalent,  20 
Joule's  heat,  110 
Joule's  law,  20,  110 

Kataphoresis,  136 
Keller  furnace,  121 
Kellner  process,  110 
Kilowatt,  definition,  19 
Kjellin's  furnace,  117 
Kjellin  process,  122 

Lamp-bank  resistance,  81 

Law,  definition,  2 

Law  of  heat  summation,  37 

Lead,  99 

Lead  accumulator,  77 

Length,  unit,  6 

Litmus,  ionization,  56 

Machalske  process,  129 
Magnesium,   113 
Manganese,   122 
Manganin,  81 
Mass,  definition,  6 
Mass,  unit,  5 
Matter,  conservation,  3 
McDonald  process,  108 
Measurement  of  physical  phe- 
nomena, 5 

Mercury  process,  106,  109 
Microfarad,  definition,  19 
Migration  of  ions,  63 
Mobility  of  ions,  63 
Molecular  conductivity,  80 
Molybdenum,  122 


144 


SUBJECT  INDEX, 


Nernst  lamps,  63 
Nernst  and  Glaser  furnace,  118 
Neutralization,  definition,  51 
Nickel,  100 
Nickeline,  81 
Nitrogen  fixation,  128 
Nomenclature  of  ions,  62 
Normal  current  density,  87 

Ohm,  definition,  17 

Ohm's  law,  17 

One  fluid  theory,  9 

Osmotic  pressure,  41,  42 

Oxone,  128 

Ozone,  generation,  135 

Part-molecules,  46 

Phenol-phthalein,  ionization,  65 

Phosphorus,  129 

Physical  phenomena,  measure- 
ment, 5 

Platinoid,'  81 

Polarization,  chemical,  74 

Polarization,  concentration,  73 

Polarization  voltage  measure- 
ment, 75 

Pole-papers,  78 

Potentiometers,  36 

Practical  electric  units,  21 

Radio-activity,  11 
Radium,  11,  12,  13 
Radium  emanations,  13 
Rathenau  process,  126 
Readman  and  Parker  process,  129 
Records,  88 
Reich  process,  127 
Resistance  boxes,  81 
Resistance, 'definition,  17 
Resistance  furnaces,  116 
Resistance  of  electrolytic  cell,  83 
Resume1,   99  .- 
Reversible  cells,  69 


Reversible  reactions,  69 

Rontgen  rays,  10,  12 

Roessler  and  Edelmann  process,  103 

Ruthenberg  process,  122 

Salt,  definition,  50 

Science,  general  principles,  1 

Shade  process,  127 

Siemens- Halske    processes,   94,    99t 

101, 102,  135 

Silent  discharge  processes,  133 
Silicides,  129 
Silicon  carbide,  130 
Siloxicon,  131 
Silver,  98 
Simon  process,  122 
Sodium,  113 
Solution  pressure,  63 
Sources  of  current,  75 
Space,  5 

Specific  conductivity,  62 
Spinthariscope,  11 
Substance,  conservation,  3 
Symbols  of  ions,  52 

Tanning  by  kataphoreais,  137 
Tantalum  lamps,  63 
Taylor  process,  126 
Theories  of  electricity,  8 
Thermal  energy,  14 
Thermopiles,  75,  77 
Thomson's  theory,  45 
Time,  definition,  6 
Time,  unit,  6 
Tin,  101 
Titanium,  123 
Tarnsformer  furnace,  117 
Tube  furnace,  117 
Tungsten,  123 
Two-fluid  theory,  9 

Uraniutn,  123 


SUBJECT  INDEX. 


145 


Vanadium,  123 
Voelker  furnace,  127 
Voltaic  pile,  24 
Voltameters,  29,  79 
Volt,  definition,  1<> 
Voltmeter,  36,  79,  80 

Water,  ionization.  ol 
Watt-hour,  definition,  20 


Weber's  arc  furnace,  122 
Weight,  definition,  5 
Weston  cadmium  cell,  36 
White  stuff,  131 
Woh will's  process,  99 

X  rays,  11 
Zinc,  102 


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